tranny question?

I have a 2000 rodeo ls v6. The motor is new (long horrable story) but the tranny has 80k. I tow a tent trailor that weighs in at 2k. It tows fine plenty of power ect. After about 100 miles the tranny starts to shift oddly and get hot. The warning light never comes on but it tries to stay in over drive.
I thought towing in 3rd would help but no luck. I had a flush and filter change and added an external cooler but it still has trouble. The only difference from stock is the tires. the stock ones were 29" od the new ones are 31" od. But it had issuse with the smaller tires and towing to. Any help would be a blessing. The manual says it can tow 4500 lbs. I am at the end of my rope:confused:

What's the maintenance history on this tranny?

I know you just recently had the fluid/filter changed, but had you ever changed it before that, and how often??

Is this all *new* since the install of the new engine? Or has it been ongoing for a while?

The difference in tires shouldn't have anything to do with it; my truck came stock with 29" tires, I've been running 32" tires for over 4yrs, and I've pulled a load twice as heavy as yours for over 60% of my trucks 183k mile life with the automatic being original.

I'm wondering, if this all started after the new engine, if they lost some ATF fluid at the time of the swap and didn't refill it, this will burn that tranny in quick order. Or, if the ATF fluid was left in the tranny too long; i.e. these tranny's need partial ATF fluid swaps every 15k miles, or tranny flushes every 25k-30k at most....but I would NEVER flush an auto tranny again, period.

Also, was your coolant system flushed at the time of the new engine, i..e what condition is your radiator in?? Also, next time you drive the truck, take a look at your volt gauge, if it's down near 12V's, let me know.

Keep us posted.....

Also, was your coolant system flushed at the time of the new engine, i..e what condition is your radiator in??

This is what I'm wondering. Where is the coolant temp when all of this is going on? I'm wondering if the rad has enough deposits to compromise the tranny fluid cooling.

IT HAD 50 K ON IT WHEN I GOT IT. I DID A FLUSH FILL AT 51K. IT LOST A HEAD GASKET AT 56K.:headshake GOT IT FIXED AND DID A PARTIAL ON THE TRANNY. THEN IF THAT WAS NOT ENOUGH IT DROPPED A SLEAVE AT 69K.
SINCE I HAVE OWNED IT IT HAS NEVER WENT OVER 3/8 HOT EVEN IN 105 TEMPS. THE RADIATOR WAS REPLACED TWO DAYS AFTER I GOT IT. BUT I DID NOT TOW ANYTHING WITH THE OLD MOTOR.:confused:THIS ONE HAS NO VOLTAGE GAUGE.

Sounds like the rad is ok...

What about the thermostat, has it been replaced AND is it an OEM Isuzu one?

The aftermarket thermostat's do not keep these engines cool enough...have you checked your antifreeze level?

factory replaced thermostat

Try double checking the ATF level too see if it's low, by chance.

I Checked The Levels Everthing Is Good.thanks For The Info. Its Going To Have To Get A Check Up. I Am Going To Take It To A Shop $

Let us know what the outcome is??