Finally got truck running after a long time down. First few test drives it sounded like belts squealing in the rear end. Then after about 10 miles while in fifth gear it started shaking like a dog trying to pass a peach seed. Shifter shaking too. While in gear is shakes in every gear, even starting off, take it out of gear and coast and it is smooth again, put it back in gear and the shaking starts again. Drained rear end and it was "over full" and was a gray sludge. U joints are tight. Ideas?