I have a 2001 impala that I am very fond of but I am having a little problem with it! While running at an even speed or coasting it does not vibrate at all but as soon as it starts accelerating it seems as if the pavement gets rough or the tires on front are out of balance. I took it to a mechanic and he first said it was skipping but when he hooked the computer up it did not show a skip. He then said he thought it was in the transmission. I really don't want to have the transmission rebuilt. It shifts really well and I don't see any problem with it. Any help will be greatly appreciated!

 

seem like you have it narrowed down to either an engine misfire or torque convertor clutch shudder.

if the mechanic cannot find any misfire history...its probably the tcc. One possible fix attempt would be to do a complete trans fluid exchange using only oem dexron vi fluid. It may improve after some driving. There may be a tcm reprogram but you would have to check with the dealer.
Others have disabled the tcc but for me, if it is occurring infrequently....I would keep driving. If fluid or reprogramming do not fix it....your into a rebuild to correct it.