Buy a laser thermometer to measure the actual temperature of the wheels + hubs. They're $20 on amazon and rather accurate - https://smile.amazon.com/s?k=laser+t...ref=nb_sb_noss
And they're great for pinpointing temp at a specific location.
Are all wheels warm or is one warmer than the others?
Front axle = Dana 60?
Rear axle = Dana 60 full-float or semi-float?
Fluids at proper levels?
Here's a DIY approach:
Besides the friction modifier idea, elevate each wheel and rotate. Is one wheel different?
Next try to rotate with the wheel-tire removed and caliper off the rotor to eliminate those from the equation. Is one wheel different?
If you're unsure if the bearing preload is correct, the front wheels should turn about half a revolution with proper preload on the wheel bearings .
The rear wheels should be the same, but it's been quite a few years since I rebuilt the hubs on a full-floating rear axle.
Go for a drive and when stopped, measure + record the temps for each wheel-hub.
Can one person drive slow while turning left and another person walk along and listen for the sound at each wheel?
A hollow tube (e.g. heater hose) that is held to the ear can help pinpoint the source of a sound.
you have one of these