I just purchase some Pirelli Pzero Nero P275/40s for my rear tires and at high speeds near 75 around overpasses I get this terrible high frequency vibration from my back rear tires. Dealership wouldn't address since they are not stock tires and technicians can't drive above 70...Any ideas? Could it be the VDC?

 

Wheels/tires are probably out of balance. I recommend you find a tireshop that has
a hunter balancer (roadforce) and get it re-balanced. should fix it.

 

Anyone know a good tire shop in Phoenix?