'97 yukon 4wd issues

I flip the switch from 2h to 4h while driving (<30mph) and get some noises (squeeking) and serious resistance on my passenger right front... enough to almost pull me off the road. when i switch back into 2h, it does not disengage (i only rolled about a 10th mile)... i put the truck in reverse, back up 10ft and then drive and it is disengaged. i do not believe the previous owner engaged 4wd very much and i did not try to shift into 4l. any suggestions? thanks