My buddy had a problem with this. Turns out he had somehow ripped the abs sensor wire. If your truck is 4x4, you should have sealed hubs, and the wire is connected to these. If whoever replaced your hub didn't correctly put the wire back up into the holders on the inner fender, then a wire could have drooped and rubbed against something, slowly wearing it down until it finally tore completely. As Pat said, follow the wire and look for any breaks, or loose connectors.