98 Ram tranny problem?

I have a 98 Ram 1500 Quad Cab 4x4 with 62,000 miles on it that is making a strange noise and vibration, sounds like someone is bouncing a basketball on the floor of the truck. The noise and vibration starts at 45 mph and will stop if I accelerate or remove my foot from the gas pedal. The noise and vibration has also happened at 55 & 65 mph.The trans does shift smoothly like it always has.This happens with the cruise on or off and with the overdrive turned on or off.

Thanks
Don

Doesn't sound like the transmission is responsible.

Did you check under the truck to see if you've got something hanging under there that shouldn't be?

I checked under the truck before I submitted the problem and found nothing loose or out of the ordinary .

I had a 2001 pu with a similar vibration and noise. When I finally found it it was a bent drive shaft. It was not bent very much. I didn't even see it when I had it up on jacks running in gear the first time, but the second time I did.

I have checked under the truck and nothing is loose, bent, or broken. This problems always happens when going up hill.

may need to replace your u joints