2001 Jimmy shuddering upon acceleration

I bought my Jimmy used almost 5 months ago and have this on going problem. When I stop at a traffic light, upon acceleration it feels like my rear end drags or shudders for a few seconds and then resumes normal function. It only happens on a straight away, if I'm making a turn from the intersection I don't seem to have a problem. I had it to the service department quite often. They drained the transfer case twice and refilled it with fresh oil with no effect. Then they ran a diagnostic check which resulted in them replacing the clutches. Then a new problem arose which was a loud whine from the front end which resulted in them replacing bearings and pinions. They assured me no more problems! Well I took it home and that rear end shuddering is still there! Can someone help me out here? :banghead: