There is nothing wrong with a proper built 4L60, a few minor upgrades and it can be as stronger as needed. Would be nice to have the deeper first gear.
The 4L80 is a monster, LOL, a shift kit and small internal mods you are looking at supporting 800 plus HP.
Wiring is easy to convert. 60 to 80 you pull 2 pins from trans plug and turn them into the ISS. Then you swap 2 more. At the ECM you swap a few as well. Then its a reflash for 80 trans segment. The way to tell if the correct segment is in, whats it commanding in 1st? On on or off off. 60 is on on.