I had this problem when i put new 22's and nitto tires on my turbo. After a bunch of visits to a few shops for road force balancing, checking to see if the rims were bent and a bunch of cash i found the problem.

The tires sucked and were the problem from the start, changed to scorpions and had no issues. Smooth as glass upto 140mph.

 

I had the same problem with two sets of factory wheels ... and several sets of tires. I tried everything ... speed force balancing ... new tires. new wheels, etc. What fixed it for me was.... making sure the lug nuts are tightend to 118 pounds (or something like that. It is in the manual). My point is I was torquing mine to 96 (like my old 964) ... and I tightened them mostly while they where on the jack with no weight on them to get them properly cenetered. Give it a try. It is free, and it worked for me.