bad vibes...brake related??

[1badv10]

while driving home the other night doing about 50mph my truck started shaking like crazy! thinking i burned thru a spark plug wire again i put it in neutral... still there /forums/images/graemlins/angryfire.gif i pull over grab my 4-way and check all the lugnuts, all fine. so i pull out and start driving again, no vibration hold 50mph for a couple mins and it comes back /forums/images/graemlins/thinking.gif pull over again and my friend that had been following me climbed under the truck for a look around.. says everything is ok.. i asked him to just touch around the axle tube(just replaced wheel bearings) cool to the touch. then he touches the vaccum plates and one is way hotter than the other.... any ideas /forums/images/graemlins/1zhelp.gif /forums/images/graemlins/1zhelp.gif ebrake cables?? i did use the ebrake before driving.. havent had a chance to pull drums yet, just wondering if anyone had any similar problems... thanks guys