I'm having the almost same problem as ravanor with my Pro-Race 2. The RPM lights are maxed out at all times due to SimDash reading the cars at 43,000 rpm when in idle, should be 4300 rpm. and of course you only can go to 30,000 rpm in Simdash.
I think it could be the game that changed how it outputs the info because DashMeter Pro has problems as well with the rpm readings.
Maybe doing as ravanor has said, removing the rpm limit in Simdash will work as a work around until this gets sorted all out.
Oh the joys of Codemasters lack of coding skills
