I am switching from a 3.9 to a 5.2 , am I going to run into any problems ?
I am getting the whole donor truck.

bigger motor possibly clearance problomes dont qote me on that just i recomend u do the measurements and check to makeshure it will fit

There have been others that have made this same post, you may want to do a search for a complete discussion. You will need complete donor vehicle of the same year with Engine (duh), transmission, driveline, complete wiring harness/ computer and exhaust system (if the v8 exhaust is bigger). All of the small parts such as air shroud for the fan, air cleaner etc. Some of the v6/v8's used the same trans (manual) , usually the v6 used the A-500 automatic and the v8's use the A-518 automatic.

Just Curious, Would you need a new rear end to handle more power or is it sturdy enough. It might be the same one for all I know. But usually IN CARS they're not when you're swapping a v6 for a v8 (common sports cars Mustangs, Camaros, etc).

id say no