Keep in mind that unless the drivetrains of the two trucks you're combining are exactly the same besides the transmissions (differential gears, engine, '96-'97 vs. '98-'00 PCM, etc.) you could have issues using the donor PCM and/or harness. Even if everything is the same except the differential gears you'll still have to re-tune the donor PCM to correct the speedometer and shift points. Gauges might be wired differently between years as well, I'm not sure. It might be easier just to keep your PCM and harness and wire in the input speed sensor for the 4L80E, then get the PCM tuned to control the 4L80E instead of the 4L60E. The input speed sensor is the only wiring change necessary at the PCM harness plugs, and it's just adding two wires and pins. The rest of the wiring can be done at the transmission end of the harness. Just throwing ideas out there.
You'll also have to move the transmission crossmember back a little on your frame, plus get a shorter rear and longer front driveshaft. Cooler lines are different as well.
I have a 4L80E swap thread here, but it was in a '97 C1500 so you'll have to deal with some things I didn't. Same year truck though, so I can help you with pinouts for the input speed sensor wires if you decide to keep your factory PCM. My factory service manuals have pinouts for all the '97 PCM harness connectors.
https://www.gmt400.com/threads/97-c1500-4l60e-to-4l80e-swap.38819/
Good luck with the swap! It's a good bit of work but IMO it's worth it if you plan on using the truck hard at all. The 4L80E is a great transmission. There are a few other members here who have done the same swap that I'm sure can help you as well.