RE: AWD astro to 4x4
Well if it is like the 98 and newer bravada then it uses theNP-136 which is 2wd until it detect wheel slipping. This was added starting in 98 to help with gas mileage. It is by default rear wheel drive so it is really a4wd rather than awd like it is called.
1997 Olds Bravada AWD 4.3L Auto ~44000mi(high idle time), CAI, Quad Beam Mod, all Synthetics Fluids