[dentheman]

Is it accurate at idle in neutral, but not when riding at speed? This could confirm if the problem is the tach or the clutch.

After reading through your posts it appears you have two tachs that both read high, suggesting the clutch is slipping. I guess one way of checking this is to get to cruising speed, then close the throttle to see if the tach drops to match your coasting speed, or even reads low. This would mean the clutch is slipping. If you can do this on a down-hill so as to maintain a fairly constant coasting speed with the throttle closed it would make the comparison easier.