Trans won't upshift, key gets stuck

Hello and any help provided will earn vast amounts of good karma! My wife has a 99 passport (Rodeo of course), DOHC v-6 auto, and pulling away from an intersection a couple weeks ago it wouldn't shift out of first. I was out of town on business so she had it towed home. I did a lot of research as I just got burned for $300 shop bill on my truck when all it needed was a new battery, and I wanted to try and take care of this myself. First thing I did after test-driving it around was to check the AT-fluid (what a pain)- I even used a cooking thermometer to check the temperature. I had the engine running and in park, and it only took about a half a quart before starting to dribble back out, so I sealed and tried test driving it- it was a little better but still hesitating on the upshift from 1st, then as it heated up, not shifting up at all- again. Other useful info- had a trans service in september of last year, they replaced the gasket and filter, and did a partial flush and refill of the ATF. We had taken it then to AAMCO as the key wouldn't release in park unless we shifted back and forth thru the gears several times. It's doing that again, and now the trans is acting up and I find it hard to believe they're unrelated. AAMCO kept it for 3 days and submitted it thru several tests and in the end said they couldn't find anything wrong with it. We keep up on maintenance with it though I don't know if the original owner ever did any trans maintenance.
I've read numerous posts with similar symptoms but not exactly same so let me summarize;
When cold trans shifts just fine;
At operating temperature starts shifting rough from first then stops shifting out of first at all or takes a long time and high rpms.
Had the fluid replaced and the shifter-linkage checked with no problem found.
Several times since we've had it the key won't come out of the ignition until we cycle thru the gears a few times.
Checked the battery voltages- off=12.4, running =14.9, haven't had the alternator checked yet as I don't know if it can make it to the shop and I don't know how comfortable I feel taking it out.

Please any help or suggestions would really be helpful...

update: after doing more research, I decided to try pulling and cleaning the range sensor, I'm in the middle of that now. Incidentally anybody know if the press-nuts(?) that the bolts for the fluid pan thread into can be replaced? I'm assuming and sure hope so- while I was under there I thought I'd make sure they were all torqued out right and one of the bolts is spinning freely- I think it happened the last time I had it the ATF serviced...?

I kinda had a similar problem with my 96 rodeo. it turned out it was only a fluid and filter problem. changed them and no more problems with the tranny. Your key issue is possible that the ignition cylinder is loose or the park safetyswitch. check inside your your steering collum. beware the yellow wire bundle. don't want your airbag blowing in your face.

Appreciate the thought, but after cleaning the range sensor (NSS) didn't help, I took it to a tranny place for a free diag- they said today that its definitely an internal mechanical problem and that for $298 they could drop it and do a further inspection... Don't know what else to do, don't even have that much money to spare let alone the $1700 they guestimated it might cost parts and labor to rebuild it...
As I'm upside-down on the thing anyways, I'm looking for a towel to throw in...

Does anyone think it would be worth it to try replacing the NSS?
thanks for the help anyways

Tranny place says the ATF is burnt and the only error code was a "speed" error Still hoping someone has an idea...

Unfortunately, it sounds like you're in for a tranny rebuild. I would question your last tranny service since they didn't refill to spec and didn't torque your pan bolts properly. Why don't you drop the pan and inspect it for gunk? The only thing we can do right now is speculate, which doesn't do you any good.

I would drop the pan and take a look. I wonder if they really did change out your filter last Sept.

Thanks pharm. Thats what the tranny place said too- the odd thing is that when I picked it up from the shop, the check engine and transmission lights came on, which they didn't do before- I don't know if that had anything to do with the diagnostics they ran on it or not. I was briefly toying with the idea of doing a partial flush /refill, filter change, and installing a new NSS myself just for the hell of it, but instead I'm thinking of just trading it in for a new car and taking the loss- we have a baby due in september and I just need a functional vehicle I can put a car seat in.
On the note of the last service- I don't think theres any way to really say for sure they didn't do something right, can you prove that a filter isn't new?

Before you go ANY further, have that alternator tested UNDER LOAD - just for curiousity sake, as these tranny's are known for acting REALLY weird when the alternator's output is low.

Also, do drop the pan, replace the filter, and refill, and see where that takes you along with that new NSS yourself.

Don't know if this matters two months later... but...

Our 2001 Rodeo was slipping and jerking, doing all the things everyone complains of, so I tried a fluid/filter change. BUT NOW it only goes into first and second gear, and then it won't get out of second.
So, in our case, a fluid change appears to be what caused the issue.
We've had nothing but problems with this tranny.

Brian - what has been the fluid's maintenance history for the life of the truck?

If ATF drain intervals didn't start until say 60k or so miles, one might have waited too long before the first fluid change out. These tranny's need to have their very first fluid swap by about 25-30k miles, at most, for good long lives.

If one did a fluid swap at say 100k miles and it's now starting to slip, it simply IS because the fluid was long worn out by then.

I know the owners manual does not stress this, but this transmission is NOT friendly on ATF, keep it's changes frequent and consistent. And, make absolute certain the ATF level is 100% dead-on, too little and the tranny will slip too.

This tranny is very easy to underfill, but very difficult to overfill - at least those owners who have to refill from underneith the truck.

I am the original owner of two Automatic Rodeo's, both started getting their fluid swapped at about 30k for the first time, on a T-tech flush machine; the '91 Rodeo had drain/refills from that time on, every 18-20k miles; the '97 Rodeo continued to have full flushes every 20k miles (it became the boat hauler) until it hit 110k miles.

I have continued doing ATF fluid drain/refills on this truck every 12-15k miles since 110k miles without issue. This truck has pulled a heavy trailer for over 60% of it's now 174k miles, and climbed more mountain passes from Colorado to Montana, Texas to Washington state, all through the southwestern desert, and our great southern states from the mason dixen line all through Arkansas, Oklahoma, etc.

Truck's sitting in the driveway following our current 1 day adventure up over Kenosha pass (10,001 feet), Red Hill pass (9,993 feet) and Monarch pass (11,312 feet) along our route to the Black Canyon of the Gunnison, Taylor Park reservoir and Tincup pass (12,000 feet) in beautiful southwestern Colorado. Truck hauled a load of 4 people and easily 1,000 lbs inside, running 32" tires (2 sizes bigger then stock) tranny didn't skip a beat.

I honestly believe if these GM 4L30-E tranny's are taken care of from the beginning and not driven to harshly, they will last a good long time, or at least 100-150k miles.

I am so very hoping to get at least 200k+ out of mine - her days of towing the boat are over; but she's still our Colorado trail-mountain tourist.

It's too bad you're having issues with yours - please give us updates on what the past service interval has been and what your outcome is.

My wife is the second owner of the Rodeo, so I don't know about the previous maintenance.

But we took it to Isuzu this morning, and they confirmed that it was leaking and had been overheated by the lack of fluid.
So, now our problem is that.
We were told:
-now the secondary clutch drum is dead (I thought these were only on 4X4 and AWD vehicles...?)
-accumulator needs to be replaced
-and the torque converter is burnt and should be replaced before it dies too.

All of this for only 2,800. Can't we get a reman, or even a new one, for that much? Seems odd to me, but I'm not good with transmissions.

But I will make sure to change the fluid in it every 25k miles from now on!