03 D/A Overdrive Issue

[Rock]

Was in the high country this weekend and noticed after driving 150+ miles over 2 mountain passes, the 3rd pass going down the mountain I noticed a low frequency type noise...I guess you could call it vibration. It was noticable in the cab. I had 4 hi engaged. I had tow/haul engaged to help reduce the amount of braking to keep a safe speed.

After getting down the pass to clear roads, back in 2 hi and tow/haul disengaged, I noticed the noise again around 60-65 mph. It only occured while accelerating. It also only occured at these speeds.

Back in town today and noticed it again while going up hills accelarating. I turned the overdrive off and the noise went away.

Where can I possibly begin trouble shooting? I checked trans. fluid levels 2x and it's in the hash marks...

Thanks in advance.

[More Power]

Can you rotate the front driveshaft by hand when the truck is supposed to be in 2WD? You can check this with the engine off, trans in park.

MP

[Rock]

Yes, I can turn the front drive shaft when in park and truck turned off.

What are you suggesting?

[Rock]

The noise/vibration is still continuing around 60 to 65 mph...usually only when cruise is on or when keeping a steady foot on the pedal the noise/vibration is most evident. If accelerating it goes away.

With tow/haul...it is evident as well at the same speeds.