Okay folks my 1990 Blazer has kinda fixed itself???... After all new U-Joints and rearend fix'es It still had a vibration when starting out even sometimes sounded like the driveshaft would hit the floor..BUMP,BUMP,BUMP.. Today with the 2 feet of snow in 12 hours I thought it may be a good time to lock the hubs and throw it in 4WD. Now my vibration is gone. Any Ideas..Its stock with 2" blocks in the back and 3 leaf springs in the front. 31" A/T's.