I have 33" tires and mine definately has the shakes at 40-45, I tightened the steering before (a year ago) and it seemed to work for a week but it came back. I guess I just learned to deal with it but it is VERY annoying when others are in my car and I look like I am suffering from parkinsens with the arm shaking like crazy. I can white-knuckle it and minimise it but then I get a clicking noise from the wheel trying to go back and forth and it feels bad so I just learned that that is the natire of the beast, if anyone figures it out I really want to know. With stock tires/rims I never had this problem so the tire or rim could definately be the culprit in your case.
2001 Ironman Daily Driver... 3.5" suspension lift (OME912 springs and 1" spring spacer), ball joint flip, 1.5" front diff. drop, 33"x12.5 TrXus MT, 16x10 Eagle Alloy rims, Interceptor, PV muffler, K&N air filter, Alpine Supercharger, Bilstein shocks, and some trimming.
2000 Ironman Project LS-1 VX... very slow progress but someday....... ohhhhh someday......