I just turned 120 thousand this week and strong. I did notice this yesterday that I was getting a rythimc vibration above 65 and upon de-accelerating. I relate it to bearings , differentials or u-joints. I crawled under the truck and I can grab the driveshaft at the transfer case and wobble it up and down ??? I dont think it should have that much play should it ?? Is isnt leaking any fluid so the seal is still plyable. Ideas ??