Wow bringing this back from the dead, but it's good folks are searching! I've replaced both my axles, all motor mounts, new tires and 2 road force balance and it's still there. However when I replaced all my wheels they were much better but still a little vibration (steering wheel doesn't shake, but I can feel it faintly through the steering wheel). I found that when I replaced when of my ball joints (lower) it helped too, don't know if that has anything to do with it. Looking for updates as well. But remember this, just because your wheel balances out doesn't mean it's true and straight. I doubted it was my wheels at first but when I put a different set on much were gone.

 

do you have low-profile tires? check your tire pressures and find the sweet spot. Wheel balancings may be required.