I've developed a vibration and am having a bit of an issue identifying a source. Does anyone else have any ideas?

Car: '14 MR with 77k miles. All stock except for exhaust. SST replaced @ 63k miles
Symptoms:
Most apparent @ 75+mph, not noticeably worse than normal road bumps when below freeway speeds
Feel some vibration through seat, but most notable through the steering wheel
Vibration is not consistent. Intensity comes and goes, while driving. Sometimes feels like it depends on the quality of the pavement
Car seems to send vibrations through wheel if I let off the gas around 3,000-3,500 rpm when at lower speeds
Does NOT vibrate while turning
Tends to not vibrate if I accelerate hard 60-100, but will vibrate when I let off gas to slow down
Does NOT vibrate as a result of braking

What have I done:
Alignment
Attached hub-centric rings for my aftermarket wheels (seemed to help some)
Did the 3&9 o'clock & the 6&12 o'clock test on all 4 tires to check ball-joints.
-Some movement from the 3&9 on both front wheels, but figure that's just from the steering system allowing them to move slightly
-No other movements
-No noticeable clunks or other noises
-Spark plugs recently replaced

What I still want to do:
-Get whole car off ground so I can check wheel bearings
-Check motor mounts

Does anyone have any ideas regarding anything else I should check out? How much vibration should be expected normally from this car? Through most of my ownership, I've had multiple warped rotors (my fault every time), broken spring, disintegrating exhaust, and bent rim which all did or could have caused vibrations, so I either don't know or don't remember how the Evo is really supposed to feel.

Thanks, Capt.

 

I would try and rebalance tires if you haven't or swap them front to back see if the vibration changes. Eliminate rims and tires. Check CV joints for leaks or excessive play.

 

I should say the tires have been balanced a few times recently too. That was the 1st thing I tried. It did not help

I'll check the CV though. Haven't noticed any oil, but who knows if I'd notice

 

Motot mounts could cause decel vibrations, have someone rev it while you watch the main mounts and see if there's a lot of movement.

 

I guess I never updated this.

I finally got all 4 tires off the ground. Watched engine during rev and didn't see any unexpected/excessive movement. We also watched all 4 tires for wobble as a sanity check.
Once the car hit ~30mph while in the air, a very clear thudding noise was heard from the right rear wheel. Decided to order replacement hub/bearing for both rear wheels. Unfortunately I didn't have time to replace them before I had to go out of state for a while. It'll be another month before I get back home to replace them.