if its anything like my 76 3/4 ton then put it in 4 low and pull it all the way towards you into 4 hi and then just gently push it forward into 2hi. and let the truck roll slowly while trying this is might make it easier.
or crawl under the truck and find the transfer case shift linkage, it could be bent,broken or just gummed up with crud.
and ya this is a toyota only forum pretty much so maybe go find a chevy forum.
