originally, when applying the breaks the truck, 3/4 ton 1979 GMC 4 wheel drive, automatic transmission would start bouncing, rocking almost side to side, on an infrequent basis. Now, I have noticed that it feels this way more frequently and at times it can occur without even applying the breaks. It is still not on a constant basis. When the truck hits a bump, the left front tire fees like it is slipping. I am assuming it is something in the front left tire but I have no idea what it is. My husband just died about 14 months ago and I am trying to take care of everything myself and I need help!!