The vibration is intermittent and starts at around 38 to 42 mph if I let off of the gas or accelerate it will go away. It doesn't always do it. The truck has 175,000 miles on it so I first tried replacing shocks and struts since it had the sensation of a bouncing wheel. Next I took it to the dealer since I had an airbag recall to get done anyway and had them balance and rotate the tires. I also requested that they try to diagnose the problem but they didn't even look at it. I took it to and independent shop I trust and they checked it out and said they could not find anything wrong with the front end or suspension. They suggested that I replace the plugs and any coils where the plugs looked suspicious. That did not help either all looked good but plugs were replaced. They also said it might be something in the transmission. My gut feeling is it is it is something in the driveline. On a visible inspection all looks fine. The carrier bearing has some play but I have heard this is normal play in the rubber boot. The u-joints look ok but with no grease fittings and 175K miles I would think they might be getting dry. Would dry but not completely failed u-joints cause something like this or could it still be the carrier bearing? I'm thinking about having the u-joints and carrier bearing replaced due to mileage just to see if that fixes the problem. Can anyone think of something else to try before I start digging into the transmission? Thanks in advance for your help.