I have a thread on the 4L80E swap in my red truck here ('97 C1500 4.3L).
https://www.gmt400.com/threads/97-c1500-4l60e-to-4l80e-swap.38819/
I used a $500 junkyard 4L80E that came with what I assume was the stock V8 converter, it's been working great for the past five years or so. If you want something built, I've heard nothing but good things about Gearstar and Hughes.
As tayto mentioned most of the wiring can be done at the transmission connector, and there are people who sell conversion harnesses if you don't feel like repinning that yourself. More info here, scroll down to "wiring conversion."
https://sites.google.com/site/sloppywiki/everything-ls/4l80e-info
The PCM info there is for LS vehicles, so disregard the two pins it tells you to run the ISS wires to at the PCM. You can find those two pins on your stock PCM by checking the factory service manual for your year, available here.
https://www.gmt400.com/threads/88-98-service-manuals.43575/