I had been considering swapping my 4.0L for a 5.0L but have also thought of just upgrading my trusty ol' 4.0 with a new intake, port and polish the heads, headers, etc. and figure the stock 5r55e transmission...even if I install a shift kit it wont be able to last much longer and would like to have more options when it comes to transfer cases. I was wondering if anyone can tell me what transmissions I can swap in directly or if there are adapters out there to swap almost anything in?

 

If you dont trust the 5r55e then look into a 5spd manual swap with a good clutch. You have two options behind the 4.0 and neither will be cheap.
Advance Adapters does or used to make an adapter to swap a GM 700r4 in which I hear is only slightly better than what you have.The other option is c4/c5 setup. The bellhousing needed is a 2.8 c5 and are very hard to find.You will not have OD anymore and I hear getting a converter to work with it is a PITA.

Also since both those autos wont interface with your trans wiring you would need to convert your truck to a manual trans ecm most likely.