One possibilty is that the motor mounts are bad. You can check this by opeming the hood, putting the parking brake on, hold the regular brake and put it in gear, watch the motor move as you give it a quick blip of gas. If it moves more than a few inches, all the moior mounts and the transmission mount must all be replaced at the same time. If you just replace the worst one, the stress from the bad mounts will ruin the new mount.
Otherwise, I am giving you two diagnostic walk throughs for your situation. Just follow the links below;
Saturday, March 10th, 2012 AT 4:38 AM