Back when I had a new 2008 Z06, on a car that goes nearly 200mph, it was recommended by the guys on the corvetteforum.com to check your lug nuts... Specifically, they stated that the lug nuts were to be torqued down to 70 ft. lbs. from the factory... so I bought a torque wrench and checked mine. No joke, they were all about 40 ft. lbs.! I forget the term, it might be "creep factor", that defines the fatiguing properties of "threads" when they're torqued into place... Just like in my profession of dentistry, when I screw an abutment onto an implant for a crown, I torque the screw down to 35 newton centimeters. I make the patient a temporary crown, let them live in that temp for a few weeks, and then before I take the impression for the permanent crown, I torque it down again to 35 newton centimeters... and every time, I find that the screw will tighten more as the metal threads have "relaxed". So... on a truck that can potentially take a lot of abuse... have you checked your lug nuts? I don't remember where, but IIRC, I think they're supposed to be torqued to 80 ft. lbs, right?