Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
Does it only do it when you are hauling? Do you do anything else different when hauling? Does the trailer have trailer brakes?
What year and model do you have, and engine size?
It's possible that it may be a drivetrain component that is binding, but eventually works loose enough to not vibrate- like a universal joint on your prop shaft
I've been thinking this over numerous times, assessing whether it could be transmission, driveline, or engine. Did you have any other work done right before this started happening? Did it happen before you got new tires?