Trailblazer Tachometer reading high
 

At idle, tech sets around 7,000 rpm. Shut off, it reads around 6,000 rpm. Rev engine, it rises relativel to 10,000 rpm. I pulled I/C fuse, cycled ignition on and off, then replace fuse. Tach reset to 0, but a few trips later it went back to reading high. Dealer said instrument cluster needs replacing. I hope it's something simple.