Whine - the P38 not me

I've been reading that some whine at speed seems to be normal on the P38 with many owners here. As this is my first P38 I'm trying to understand it. I have a good amount of whine at speed that I would guess is from the diff or drive train. But when I let off the gas at 55 or so it stops. Back on the gas it's there. I would wager if it is the diff or drive train it would be present even when letting off the gas. The engine is quite smooth and at park when rev'd there is no noise ala whine or the like. I changed front and rear diffs with Mobil 1 75w90 and lubed the ujoints and shafts. I'm familiar with bad wheel bearings and this is not that kind of noise. Could this be the tranny?