Welcome aboard usmc. How old is your current engine?
If you are looking for more speed Id suggest either and O.S. engine or the LRP Z.18s. With either engine you are going to have to upgrade and shim your diffs because the extra power of those engines will destroy the stock diffs.
My current engine is almost brand new. It only has about 8 tanks run through it including the break in. I had my LHS put it in when the old one died. I have another roller MT that if i upgrade the engine in my MT2 i am going to put the old MT2 engine in. I dont really need to upgrade the engine first but i just dont know what i should do first. How do i shim my diffs? Can i just buy new ones? Sorry for the stupid questions i just dont want to mess up my new truck.