1998 Chevy Suburban stuck in 4 wheel drive

I had a similar problem in my 99 Suburban. There was a problem with the transfer case motor/actuator. Sometimes it switched between 2WD and 4WD as it should, other times it would get "stuck" in either 2WD or 4WD / would not change. When it would get stuck in 4WD, I could get it back into 2WD by removing the battery cable, let it sit for a few minutes, and when I started the truck back up it was in 2WD. This "trick" got me out of a bind several times (worked every time) until I was able to replace the transfer case motor. Hope this helps.