So it sounds like it gets worse or at least changes as the load increase, is there any difference in, or does it go away if you get up to speed and then coast? I had the very same thing that manifested as a low whine/hum/“buzz” under load that almost went away at coast. Chased it for a while until it started to also vibrate slightly with the whine, only to figure out that my rear diff had bought the farm...

I too thought tires in the beginning, I actually had the place I purchased the tires from tell me it was the tires also - I asked the guy to put his money where his mouth was and throw 4 tires on the truck - if the whine stops, I buy them, if it doesn’t, you put the old ones back on and I leave - he put the old ones back in and I left...

Diff wasn’t too expensive and over all pretty straight forward to install, I think with gear oil and friction additive I may have had 400 in parts.

EDIT: You could always pull the fill plugs and make sure they’re actually still full as a starting point, just so you know for sure. May save you $60 in gear oil [emoji106]

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