I'll chime in with my experience. I had 4L60e rebuilt at a dealership at about 74,000 miles. The rebuild almost lasted that long and it wasn't cheap. Replacing it was not an option for me because it was an oddball revision. When it came time to do again, I shopped my state for a rebuilder that serviced the high performance market, offered serious upgrades, and had a very good warranty. That rebuild solved my problems and it's new owner has a great truck.
This will not be the cheapest path to go, but unless your goal is to just get it going so you can sell it, your best path will be a high quality upgraded rebuild.
If your choice is to find a salvage transmission to fit a 14 year old truck, well, a transmission isn't like a bumper or a skid plate that if it looks ok it'll be ok. The only use for a salvage transmission in my view is to provide a core for a rebuilder to work with because your original has a hole in the case or some other serious problem.