91 chevy 2500 350 4x4 shaking at about 65mph and up it shakes for about 7 seconds and then stoppes for 8 seconds and over and over and over and over again. lol but i have all new u-joints, carrier bearing, motor, tranny (new torque converter), all ball joints, cv joints, new tires, shocks, up graded to 7and1 leaf springs sits only inch higher than factory MADE FOR MY TRUCK, rear end is full, no leaks rear end feels tight. help