Between 65-80 theres a small noticable vibration in the ride but doesnt overly affect the ride quality... but once I hit around 85, the whole car shakes. Not violently, but enough to know somethings not right and is quite irritating. The weird thing is, if I play with the RPMs alittle bit, it will completely smooth itself out and ride beautifully for a few seconds, and then work itself back into a nice little shake. The steering wheel goes nuts and I can feel it through my drivers seat too. I have a stock drive shaft, tranny and engine for the most part. Only upgrades I have are springs and shocks (and rims, which have been balanced). Any ideas?