speedometer and tach read high

1998 GMC Sierra 1500 v6 4x2 automatic.Hello everyone ,I just recently inherited this vehicle and its in great shape except speedometer reads way high (0 at idle then jumps way up as you start moving)and tach shows around 3000 r.p.m. at idle then rises.I have used a laptop and obd2 adapter and it shows the correct R.P.M. as well as correct SPEED. So I'm assuming IPC . I am trying to pin point the faulty component or components. I have checked the two stepper motors and they seem fine compared to a good nearly identical stepper motor.I read elsewhere these could be a problem. My guess right now is the problem is on the small circuit board incorporated in the IPC. Does anyone have any information on this problem or what components may be at fault.Or am I way off target on this . I've searched around quite a bit and other than all out replacing the IPC I haven't found much about what the actual problem is with the IPC. Thanks for listening any responses are of course greatly appreciated :1zhelp: