Can the transmishon be removed on a 2006 pontaic grand Prix 3800 without removing the engine?

Yes the trans can be removed. I will explain later today the process.

Yes. It's a fairly major project though. Should be able to find a you tube video on the subject fairly easily to help you decide if you can do it yourself or not. You'll need jack stands, some sort of transmission jack (which you can rent), a decent set of wrenches, sockets etc. If you have air an impact wrench will help, and a helper to help with some of the heavier and more awkward components will help too. As a do it your selfer plan on 15 to 20 hours.