on the way to gilmer, last saturday, i started hearing a very noticeable roar and felt some vibration to go with it, at speeds above 70mph. i figure it has to be something in the driveline, since it only does it when i load it up. coasting downhill, or when i let off the gas, it improves, so i ruled out tires. it goes away when i slap it in neutral, so it's not the engine. since it's sort of nasty outside, for texas, right now, any suggestions on a fast, easy way to check for the problem? i really don't feel like laying under the thing on damp/cold concrete for extended periods of time, especially since i get home well after dark. the truck made it through the whole day of wheeling and back home without incident. 400 mile round-trip. i'm just really hoping i didn't bend my frame or bash up a driveline component, the week before, mudding. thanks in advance.