Truck Repair: Dodge Ram 2500 vibration, dodge ram 2500, power steering pump

Question
I have a 2002 Ram 2500 with at cummings 24v diesel.  I am experiencing a vibration that only starts at about 65mph and gets worse up to 75mph. I do not feel it in the steering wheel, and it is ther wheather the truck is in drive or nutural. I have had the tires ballacned twice and have replaced the u-joints. I was planing on having the drive shaft ballanced but I have a feeling it won't help.  I bought the truck in November and the problem didn't start until March when I had the power steering pump and belt replaced.  I don't think this has anything to do with the vibration, but I am running out of options.  Thanks for any advice you can give me.

Answer
Does it get worse past 75 MPH?Not in steering wheel eliminates frt tires & such.If it is a two piece driveshaft,make sure the driveshaft is timed(yokes are lined up with each other).That will surely cause a vibration at higher speeds.I pretty sure the P/S pump should not effect it or the vacuum pump that drives it.Possible misfire under a load or low fuel pressure to VP44 injection pump caused by the transfer pump,stopped up fuel pressure,or air in suction line.Have not seen any vibration dampners go bad on the B engines,but there is a timing mark on the dampner(looks like a small chisel mark on the inside piece that should line up to a small chisel like mark on the outer part).If they are not lined up,replace it.