The '96+ 4.3 is junk and likes to spin bearings. My Blazer spun one at 123k and a month after putting a junkyard motor in it the tranny started slipping on hills and blowing out fluid. Then the heater core popped while looking for a new car.
Most are push button 4wd (on dash). Thats what my brother's '95 and my '96 Blazer had. Some of the base models had a floor shift though.
The 4wd actuator on the front axle went bad on my brother's truck so the 4wd didnt work. He traded the truck in with it being bad.
Check for rust at the floor/firewall seam. My brother's floor kept getting wet on the passenger side and we found out why after pulling up the carpet- the seam rotted out.
If the truck has over 100k plan on replacing all the ball joints, tie rod ends, idler arm, pitman arm, etc.
Ive owned two S10s and a Blazer and my brother had an S10 and we had to replace all those parts around 100k.