I have an 06 s Auto and i have been having a problem where after idling for a bit such as at a drive through and sometimes even at a long light, when i start moving the shifts become very erratic and kinda snap the car forward. i thought it was my battery at first because i had an issue with a dying alternator and when my battery was close to dying it would have the same symptoms. but after changing my battery yesterday (alternator has already been changed) the problem still persists. any ideas on this problem? Thanks!

 

Your valve body is worn out, most likely. Starting reading the giant thread below.
Find a shop, order reman valve body, get it installed, pay about $1500 and life will be good again.

 

well yesterday i checked my voltage and it was at <12.4 at idle. so it still seems like an electrical issue