Vibration/Wobble at high elevations + acceleration

[DriverX]

Hello,

I am stumped. Since February I have been having a vibration/wobble when accelerating or let's say going up hill at high speeds, but only at higher elevations. And even then, it takes a while to show itself, but once it develops it continues at about a 100% success rate. Then a few weeks at home at low elevations and I just can't reproduce it.

It feels similar to a wheel weight balancing issue, where the front right passenger can feel it strongly and I can feel it in the steering, but no one else in the car really notices. It typically starts 2-3 days into road trips to the mountains or high desert and continues until we get back down to near sea level.

It is felt only when pushing the gas to accelerate, or go up hill at higher speeds, say 40-70. It is not felt at lower speeds, or at high speeds while foot is off the pedal.

Since then, we have tried rotating the wheels a couple of times, and have also replaced the engine and transfer case mounts. But it continues.

I've checked the wheels for play but don't find much. No cracked CVs or grease spray or anything obvious like that.

Any ideas?

Thank you!