Help my tranny!!

For the past 3 or 4 weeks, my car has been "bucking" ever so slightly going up hill at about 30 to 35 mph. The bucking was very week, and almost un-noticable. I decided to take it in to my local GM dealer service center to see what they had to say about it-- just to be on the safe side. They scanned the computer and no codes have been generated at all. They test drove it and couldn't duplicate it. The service guy said it must be very minor, since there are no codes in the car. They suggested that it may be the plugs and wires, or dirty fuel injectors. I said to change the plugs and wires, and I had them do a transmission flush. After 4 hours, they called to say that my car was ready.

I paid and picked up the car, drove it home (less than 1 mile) and parked it for a few hours. I decided to take it for a test drive to see if the bucking has disappeared. It had. I was happy. Until I came to a stop light in town, and started to drive. Now my car shifts very hard-- to the point it feels like I just got rear-ended, or went over a big bump in the road. I slowed down a few more times and each time I started, it would shift very hard, usually around 20-25 mph and then again around 40 mph. (Also, the car has to be hot for the hard shifting to occur, starting out from cold start, there are NO hard shifts). I had never experienced this before and now a new problem has occured.

So I took the cat back to the dealership where they hooked it up to their computer again. Now there was a code for some part of the transmission, which he told me was going to cost $1200 to repair. Not very happy now. I also called onstar from my car, and had them run a diagnostics check, and they found NO trouble codes. So this also concerns me that Onstar didn't find any codes in my car, but my dealership did.
I thought that this was VERY coinsidental that the very same day after bringing my car in to get new plugs and wires and a tranny flush, that a brand new problem has occured, which I think the mechanic had messed something up. Not on purpose, but may have done something wrong, or there's a bad wire, etc. It's just seems wierd that this new problem occured.
The service guy said that this new problem is unrelated to the bucking. And it has nothing to do with what they had done to the car the previous day. I find this a little hard to believe, since I have never experienced hard shifting in any of my pontiac cars. Could it be a fluke coinsidence? I suppose, but to me it it just way to fishy. Any comments? Should I get a second opinion from another mechanic? Am I screwed? Should I go back and complain? I truly think that the mechanic did something wrong, and now they are trying to get more money out of me, or are trying to cover their mistake up.
Please help me out!

PS. From another forum, I was told to never FLUSH the tranny. It hold certain oils, etc, that actually helps protect the tranny... I hope that wasent my fatal mistake that led to the 2nd senario!

What year, model and engine and how many miles?

OnStar may not pickup Class "D" odb-ii DTC error codes unless they trigger a SES light. A Tech II or a capable scanner is required. A lot of tranny fault codes are Class "D" and the code will be stored for retrieval.

What was the DTC error code found by the dealer? If tranny related then the hard shifting is a result of the fault. High line pressure is commanded and as a result you get that problem. If the code(s) are P18XX it may indicate a bad solenoid such as pressure control (PCS). That should not cost $1200 for replacement and labor.

Take it to a reputable tranny shop other than dealer and have them scan it with a trans capable scanner. Most tranny shops charge around $500 for replacement of the PCS and labor.

BTW - Depending on your mileage the flush may have exacerbated the original problem. The general concensus is not to do a flush either full or fluid exchange.

Thanks for the reply. I forgot to mention I have a 2001 GT with 64,000 miles.

I am not sure what the dealer said that the code was. I am planning to go to another mechanic to get my car scanned again and get another estimate on repair costs.

I know that my "check engine" light has never lit up since I have owned the car. The dealership even said it is an intermintant problem right now, and my engine light will probably not light up.

Will adding any type of "transmission additive" from AutoZone, etc, help at all? Or should I not even take that route?

Thanks again

Thanks for the reply. I forgot to mention I have a 2001 GT with 64,000 miles.

I am not sure what the dealer said that the code was. I am planning to go to another mechanic to get my car scanned again and get another estimate on repair costs.

I know that my "check engine" light has never lit up since I have owned the car. The dealership even said it is an intermintant problem right now, and my engine light will probably not light up.

Will adding any type of "transmission additive" from AutoZone, etc, help at all? Or should I not even take that route?

Thanks again

I found that Sea Foam is the best initial additve to use (8 ounces) then followup after 500 miles with Lubegard. Sea Foam is normally stocked by NAPA Auto Parts. LubeGard at Pep Boys or AAMCO. You have nothing to lose and hopefully with your mileage it isn't too far gone so the additive may help.

BTW - The additive will cause the ATF to go over the top line but that is OK. I've gone 16 ounces over with no adverse effects or any fluid coming out the tranny vent. It is not necessary to drain any ATF before putting in 8 - 16 ounces of additive.

it does seem like the flush was a bad idea and if that is all the dealer did to the tranny i would point the finger at them. not that it couldnt be something else, it just sounds real suspicious, and you would think with 64k on it that the dealer of all people would have know not to flush it, but i guess that is how they make their money, and it probably is sop.