You will hear a different view on the 6.2 from every person you ask. It takes alot of maintenance, but will last forever. If the PO didn't maintain it, expect it to go soon. If you don't maintain it, expect it to go soon. If both you, and the PO, keep/kept it well maintained, you'll be happy with it.
I drive a 4-cyl MJ on 31s, regeared, with an auto and I wouldn't recommend it. My mileage has never been that great to warrant the lack of power.
A 4-cyl stick might be okay for you if you keep the tires small (2wd).
That GMC isn't a bad price. 4x4?