I have an '08. It's off the hook. I have the 4wd, but not the Z71. It rides sooo smooth for a 4wd. And it knocks down an average of 19 MPG when not loaded or towing. A major step up from my previous truck, a '99 F150 V-6. BTW, the 5.3L is the way to go. If you aren't getting the 4wd, the rear locker is a must. In short, the only thing I don't like about it is it doesn't quite idle smoothly. But that probably could be easily fixed with a tune.

 

Its just my opinion, but I think you are over looking the major question here. How much are they willing to trade you for? That would be my MAIN concern.
If you have a chance to move UP that many years, and DOWN that much in mileage that would be the only thing I would be considering right now. Once you figure that part out, then I would ask myself IF it is worth it or not.
But then that's just me. If the deal is good enough I will trade my truck today. If not, I will drive it for ten years. It is all about the cash to me.
I do agree however you really HAVE to have the G80 locking rear end if you go 2WD though. I drive a 2X4 as well. I have never had a need for a 4X4, but I would not buy one without the locking rear end. Again, that is just my opinion.
Good luck to you in what ever you choose to do.