GMC Envoy 6 Speed Auto Trans Swap?

[PaulEd]

We have a 2005 GMC Envoy, with the 4.2 liter, I-6 motor, and 4 speed auto trans, and 4 WD, that gets 18, to 21 mpg, at best.

Is there a newer year, GMC 6 speed, auto trans, 4 WD, that is, more, or less, a "Bolt In" swap for our GMC Envoy?