96 jimmy 4wd issue need help

[Abrough61786]

Ok so im new to the forum and need some help with an issue on my 1996 GMC Jimmy 4.3L V6. It is an automatic trans with the stick shift T case (not the push button one). My issue is the front wheels will not spin/ work in 4wd Hi or Lo. I have replaced the three vacuum lines going to the T case as well as the T case vacuum switch. Also replaced the vacuum actuator and actuator shift cable. Last I tightened and greased the linkage. Everything seems to work, all the indicator lights work, it shifts into 2wd 4Hi and 4Lo , and the actuator is moving indicating I have vacuum. I also put the truck on a lify and went though all the gears . The T case works and both the front and rear drive shafts spin. However the front wheels do not! Im thinking its something wrong with the front axle in the diff or maby the hubs but cant tell without ripping it all apart witch I dont want to do untill I got a better idea of what im getting into. I just got the truck and this was one of the reasons i got it so cheap. I have tryed to find some diagrams and exploded pix of the front axle to help me but no luck. My chiltons book dose not go into the breakdown of the front axle. Id really like to get some help and would be greatfull for it. Is it the hubs? is there some kinda relay or something i may have missed? could the fluids being low make it do this? what is in the diff that makes the 4wd work and could the gear be bad? would be great to get a few pix so i know what to look for and any tips on things to try. Thanks