Burning Rubber Smell (not joking)

[toddtheodd]

I have a 72 c10 lwb, and when I am doing about 60-70 I can start to smell what smells like burning rubber smell. Gets worse if I go faster.
I can smell it better if I ONLY have the wing window open partially.
I've checked my spark plug wires, and other wires under the hood, but they are all fine.
I have replaced the front calipers, pads, and rotors, but no change.
When changing the rotors, I replaced the bearings and grease, and packed the crap out of it, but no change.
Also, around 85ish, I get a hell of a vibration. I've checked the tire balance, and of course like I said I replaced the bearings, so I don't know where the vibration is coming from either.

What could be causing the burning rubber smell? At 70ish?

Could the u-joint bearings for my driveshaft maybe smell like that if they need more grease?

I am also suspicious of the transmission may be going out, though I am not having a problem with slipping or popping out of gear. I'm supposed to have a 2400 stall torque converter, but it is still the stock stall.

I'm at my wits end here.