what up, I have a 2001 LS impala 3.8 V6, with 126,000 miles. I currenly have the car under warranty and just wondering what could it be. Whenever I go and it's shifts it would jerk every time it shifts gears, it never does this when i apply more gas and the automatic transmission downshift, only when it upshifts. This happen one time recently but it started again today, not everytime I drive. Please help, so I know a little something before taking it in to have it look at.

 

Could be a worn motor mount/anchor. Not sure what the engine mount setup is on these cars, but there is probablly one main mount towards the front of the car that mounts to the bottom of the engine.

Always check the cheap things first ;-)