I have 2005 6 speed ( I know, I have to update my signature ) Anyhoo,
I have a vibration of sorts while traveling on the interstate. It feels as if I am driving on the rumble strip, just not as severe.

It started about 2 days ago while pulling my empty dump trailer. ( 3,700 lbs) I thought it was just the trailer vibrating the truck. Then on the way to work it progressively got worse to where it does it almost all the time. like i said it fells just like riding on the rumble strip, just not as bad as that.
Hopefully it is just the U-joint in the drive shaft but if anyone has had this problem before,, I am all ears !!!

 

if it gets alot worse when you let off the accelerator, def. a u-joint. if it is only at certain speeds, it could also be a tire problem, if it is four wheel drive it could be the stabalizer, have you rotated tires recently? Mine did that and it was I tire, but the 03 did it and it was a u-joint at 12,000 miles, so?

 

Maybe it could be all the snow up under the truck if I am really lucky. I only have 18,000 on mine. It doesn't seem to get any better or worse when I let off the go pedal. Yesterday it only did it once in a while. Now it does it constantly. Hmmmm????

 

Shake the drive line then look at your rims. You may have some snow, ice, mud on them creating an imbalance. I can't tell from your post but are you still towing the trailer. Believe it or not, you can feel an out-of-balance trailer tire when the trailer is empty if it's bad enough.

 

No, I'm not towing the trailer. It seemed to get worse after I dropped the trailer. I live up a 2.5 mile driveway up over a mountain and it is severely drifted with snow right now. Hopefully you are correct about the ice and snow.
I gonna put it in the garage tonight and turn the heat up in there and hopefully melt it off the truck then see what happens.

 

Fingers crossed here. Hope it's that simple!

 

My vote goes for a bad u-joint. One way to easily check this is not only to shake each u-joint as has already been mentioned, but go for a drive and then immediately afterwards crawl underneath and put your finger on the end cap of each u-joint brearing. If it is a bad bearing, chances are one bearing will be considerably warmer then the other three.
Of course it could also be something as simple as mud or snow building up off center inside a wheel or even two wheels.

 

Found the problem. The deep snow pulled the rear exhaust hanger out and the pipe was vibrating at certain rpms. SWHEEW !! That is a relief..

 

Lucky you! Glad that was all.