Maybe it's an ex that you ran over a week ago?
Seriously - check to see if something is caught on the truck and is dragging on the road - or something loose that is catching air and rattling like crazy. Also, watch your engine RPMs to see if that is running higher than normal. It if is, you could have an issue with the transmission or shifter (auto trans).
Ive been under the truck, nothing is stuck. But, it does shift from first to second hard, and it will hesitate from 1st to second when it down shifts coming out of a turn. Id almost rather it be the rear end than the trans. Ugh