Replacing trans myself?

I have a 95 sonoma and my truck had 150,000 miles and just about everything in the motor was worn out or broken so I rebuilt it with a long block (shoulda went bigger right off the bat but I didn't) so anyways now I have 4 grand into the motor and the trans is starting to go. I've talked to some people at different trans shops and they say to have it rebuilt because it is 4 wheel drive it will be like 2 or 3 grand. I was wondering if it would be worth it for me to go to a scrap yard or something and get a trans from there and switch them out myself or just let the pros do it. I rebuilt the motor so I a mechanical but I didn't get to the automatic trans class in school so I really have no idea about trans work. I believe there is the 700r trans in my truck. But then I don't know if there is a problem with any of the 4x4 stuff either. I have the truck up for sale right now, but I am really considering doing the trans for how much money I have into my truck. So if any of you guys have any advice I would appreciate it.

rebuild it and sell it, no question

I would just get another out of a wrecking yard that has a 30 day warrentee and repalce it my self and save a grand or 2 in deinstallation and installation charges. I had a 94 S-10 and the 5 speed tranny went out at 199K miles (in 1999), they charged $950.00 to take it out and put it back in and $1200.00 to rebuild it. (I was thinking $600.00)
I would sell it with that tranny and the new owner won't even care, or I wouldn't as a new used car owner.