I am having a similar problem with my 2002 alero. When it shifts into 3rd or 4th gear it does that bucking that you describe. Did you find the problem with yours? I have a suspicion that it has something to do with the torque converter not locking up. It will eventually plane out and then stay locked up. If my theory is correct, does anyone have any idea what has actually failed or how I should approach this repair? I know there is a valve that can be replaced. Is it possoble that it is failing? I would like to be able to unplug it to disable it from locking up to see if that does anything. Where do I find this valve and the connection for it?
Thanks