A friend of mine locally was selling a similar van. 2003 AWD with 83,000 miles, conversion van interior, barn doors both sides, and even a D80 Posi rear with 4.10 gears for $8300. I almost bought it, but the rust looked pretty bad underneath and it scared me off. Nice van otherwise, though, and drove very nicely compared with my E250.
AWD was offered on Chevy Express and GMC Savana brands. Not sure if the range of years when it was all offered, but somewhere betweeen 2002 and recently. I don't think they offer it any more? AWD is basically always on, and automatically sends power to wheels that are slipping, rather than sending power to both axles at the same time regardless of slipping like 4WD does when engaged. 4WD also usually has a high and low range, giving you extra-low gears if you need them. With 4x4, if you don't have limited slip or locking differentials, you really only have 2WD (one wheel being driven in each axle).