How do I go about removing the speed restriction on a 2005 STS V-6. I heard about the tire ratings or whatever, but I have 22" ZR rated tires "A" Temp & "A" Tread ratings and I am limited to 121 mph at 4200 RPM's. What can I do or who can I get to increase the speed. I've read stories of the V-6 topping 148 mph. Please Help!!