It sounds like maybe some sort of vacuum actuator on the front axle or even a T case shift modual to me but I'm not a expert by no means.Dont even know if the Chebbys has stuff like fords do. Just my opinion from not seeing or driving it. Check your linkage also! Grease em up if they are froze or mucked up bad.
Atomic trans in Villa Park on North avenue forsure. You wont get ripped there and you can count on the price they qwote you not like some others. Ask for Frank and tell him Tom with American Exteriors sent ya. They have done about 6-8 of my trannys, transfer case, 4x4 work ect... on all my work trucks over the last 8 years. Great guys great prices with superior turn around time.