I own a '99 GC with the I6... I didn't want the 8 for 2 reasons: 1- fuel 2- the 4x4 setup is not as versatile (The QuadraTrac is actually a better system but you don't get to pick 4x4 or not). However, the rear seal can blow out and it's big bucks. With the I6 it uses totally different Selectrac 4x4 and that transmission is bullet proof.
The extra 50hp would be nice sometimes though