As far as I know, the 5.3 in the 900 platform (what you have) is the same as in the earlier versions.
You may regret the 6.0L with the stock 4L60E trans. Find a 6.0L with a trans (4l80E) and transfer case and I think you'll just need a new drivshaft, ECU flash, and some small harness mods.
If I was you, I'd junkyard a 5.3 and go right back in with it- I had a 2004 K1500 with 165,000 when I sold it and the guy is still driving it today 4 years later....same motor.
This post was edited on 6/21 at 9:57 am