Oldsmobile/Buick Repair: Car chatters/shudders upon acceleration, transmission shop, factory warranty

Question
Buick 2003 Park Avenue Ultra - car chatters/hesitates/stutters upon acceleration.  Only when you are starting from a stopped position.  Dealer cannot find anything wrong with it, been having the problem for about 9 months.  I took it to a transmission shop today, they are saying that it is the internal air pressure problem within the transmission.  An expense repair and not too common.  I hope that I am referring to the diagnosis correctly, if not please correct me.  The car is still under factory warranty but the dealer won't acknowledge that there is a problem.  Said the car is functioning normally. Does the transmission shop seem to know what they are talking about? he said that he is 90% sure that that is the problem...after driving the car for 5 mins.  

Answer
A transmission shop actually told you:

I took it to a transmission shop today, they are saying that it is the internal air pressure problem within the transmission.

That is one of the lousiest diagnostics that I have EVER heard of. If this is what they actually said, They are totally out of their minds.

I would need to drive the vehicle in order to even offer any suggestions.


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