I've had one 5.3 in a 1/2 ton extended cab that was supercharged, and a 6.0 in my 1500HD. The 5.3 flat hauled you know what! And I know what you mean about the 6.0, when pulling a steep grade with the snowmobile trailer or fifth wheel, it hits 4000 rpm and pulls like a tank.
The PCM needs reprogramming to delete the unneeded stuff, like VATS (the anti-theft), EVAP and all the emissions stuff that is not needed, set the gear ratios and tire size for the speedo, and make it's operation stand alone too. Plus do the performance tune.
The stand alone harness is easy to hook up, there are only a handfull of ignition wires, a 12v constant, and a few grounds. I don't see any reason to try to integrate it into the truck's harness, the PCM has nothing to do with any of the truck's operations. I have a 4 hole fuse block with 2 relays that I will use to hook it up. It will be very easy and clean.
8 miles huh? It's a new engine, but $3800 still seems a little steep for just the engine. I got a 58,000 mile engine and a 4L60E trans from a wrecked 2006 Silverado for $2000, including all the front accessories, radiator and shroud, yoke, drive by wire stuff, etc. These are 200,000 mile engines, so I still have ~150,000 miles left in mine.
www.specializedpartsplanet.com 800-722-6015 and ask for Paul Smith.