At a loss...
 

Within the last month I have picked up a vibration that seems to be getting worse. Unlike others (searched 16 pages) this vibration only occurs when decelerating from about 18 mph to a stop. It is also present when coasting in this speed range. I do not feel anything upon acceleration like when I had a U-joint in the rear drive shaft go out. I have checked the driveshafts and could not find any indication of bad U-joints. When I lost the rear one the seal was gone and there was a line of grease on the underside of the bed. All u-joints have intact seals and I cannot manually feel any play in them. I have a bit over 62,000 miles on the truck, it is not lifted, and it has stock the Michelins.

I don't want to just throw money into u-joints as I need to save money for a trip where fuel alone will cost me $1500 to $2000. If necessary though I will replace them as it would be cheaper than a breakdown.

On edit: Admin please place this thread in the correct forum. 3rd Gen 2003-2007

check your front tires for cupping and uneven wear.

when mine start to wear, it causes much the same problem, a rotate usually takes care of it

Recheck u-joints
 

The first time I had one go I couldn't feel anything wrong with the joint. I think I had less than 20k miles at the time. I had it fixed under warranty, dealer tech said the u-joint was seizing up. 2nd was around 40k miles. I pulled the drive shaft and everything felt fine. After a little closer inspection I fount the center joint a little tight in part of its range of motion. When I pulled it apart I found one bearing cup dry. Replaced that one u-joint, all was well afterwards.

Also, can't remember what year your truck is. mine was an '06 dually quad-cab. I found u-joints for about $50 at Advance Auto parts.

Could be numerous things equalizer.......You can try to remove the rear driveshaft and drive it in 4x4 to see if it is any different. If it's gone, you know it's in the rear driveshaft. Obviously, same thing with the front driveshaft but you won't have to use 4x4 LOL! Then I would consider looking at the rear brake calipers if it continues. I've read several posts about the calipers sticking, and just had it happen to me a couple of weeks ago. The calipers were staying on and the rear rotors had warped. I opened the bleeder on the r/r caliper and the wheel was still excessively hard to turn. Replaced the calipers and had the rotors machined, and all has been fine since.

Thanks for the responses guys. I have tried to keep the tires rotated but that doesnt' mean any more than having low miles on a u-joint. It has finally stopped raining long enough that I can go out and look at it.

Most likely I would say that the issue is in the front end. Decelerating shifts weight to the front. You might try at a faster speed and lightly lean on the brakes and see it it will vibrate.
Friends of mime was tires and he had the exact symptoms.

My buddies truck did the same thing you are describing and it turned out to be ujoints. I can't recall which ones exactly but def. ujoints. hope this helps