I have a 2000 4runner 4cyl 5 spd, and want to know if I can swap a 6cyl engine without replacing the transmission
Engine Swap from 4 cyl to 6 cyl on 2000 Toyota 4Runner
Extremely unlikely. In order to do this, you'll either need help from someone who has done some engine swaps in this truck, or you can do some research using the transmission part numbers. Either way, it's going to be complicated.