I got a 88 GMC 1500 SLX Short box and the rear axel has started locking up on me. I just got the thing not to long ago because I didn't want to use my 88 Suburban for a work truck. Is it posible that a posi can lock down the rear. It hapend once goin over some tracks and all I did was put it in 4 low and did a bit of reverse and foward and she broke loose. I thought there was some crap in the drums so I cleaned them out. Last monday we had a kickass snow storm and I had to run into town for some beer and had it into 4 high and when I went around a tight bend it did it again. WTF? Has anybody had this happen to them before? I left the truck at home and had to take the Burb to work here in Niagara and got it all coverd in salt crap. This Saturday I'm gonna get on this thing startin from the rear so if anyone's got some info to pass on it would be a great help. Thanks Max.