I just completed a trans removal & reinstallation following this process. My car isn't a Grand Prix but it has the L67 driveline and a lot of the steps are the same.
My 2002 Buick Park Avenue Ultra is supposedly set up the same way as a same year Bonneville SSEi.
The one place I really had some trouble was getting the rear bolt to release the trans from the engine. I just couldn't get a socket on that bolt. It may have been me being a klutz, but I like to blame it on the rear exhaust and the power steering pump bracket. On my car the bracket behind the pump is a good sized chunk of aluminum, and it stymied me at every turn.
Fortunately I watched a video made by a professional tech who was removing a trans from a Buick Lesabre. He got the back bolt by stacking two wobble extensions and a wobble 18mm. Then he reached up at a 45 degree angle between the trans and the engine to turn the bolt.
I would have taken that approach but since I also needed to do my oil pan gasket I dropped the pan too. Once my oil pan was down I could see the bolt.
I reinstalled the trans with a rebuilt torque converter and now I have 4th gear lock up. Fingers crossed that it stays that way.
