roar and some vibration at highway speeds

[vortec]

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.

 

[Chevy305]

sounds like u-joints to me

if they are greacable, greace them, it will make them last a little longer.

 

[vortec]

i thought u-joints immediately, and even pulled over to check, but could not detect any play at all, when trying to move them by hand. bad u-joints i've seen in the past (not on my vehicles) had a fair amount of slack. i guess that isn't always the case. i'll give them another check. thanks.