Ok, I know there are a lot of posts about the 3rd gen trucks having a rearend whine, but I have a second gen..

The whine/howl I hear is only after the truck gets at least a little warm, and only on acceleration. Going uphill makes it much more pronounced.

It's sort of a medium pitched noise, definitely not turbo whine. It almost sounds like the noise of a bad tire, but that would be constant.

There's a TSB for such a noise requiring replacment of the muffler, but that doesn't sound right, considering it doesn't do it while revving up the engine in neutral.

Could it be a u-joint? Or is it more than likely a rearend problem? I also get a chatter/ratcheting if I jam on the accelerator just as it shifts to second gear..