[skid]

1st thing is to check the condition of the ball joints, drag link ends, and tie rod ends. Also check the condition of your rag joint. Then have the alignment checked. If everything in the front is ok, check to see if how much rear axle float you have. On these old Blazers, sometimes the rear axle tips have worn against the pinion shaft in the diff causing excess end float. This will "steer" the rear end. To check, jack the rear wheel off the ground and try to slide the axle in and out. There should be only around 0.008"-0.012" travel. If it thunks back and forth, you've found the answer. Check both sides...