'88 Blazer Tachometer

The tach in my Blazer is reading high. It has slowly been increasing over time. Right now it reads 1900 rpm at idle and over redline when I shift. Can the tach be adjusted to read correctly or is it slowly dying and must be replaced?

My speedo is five over, and maybe the fact is that it has 277K on it. It can be adjusted, but i would just replace it.

My speedo is five over, and maybe the fact is that it has 277K on it. It can be adjusted, but i would just replace it.

The speedometer actually reads about 5 mph low because of the taller tires on the vehicle. My question was about the tachometer, you know, the thingy that shows RPM just to the right of the speedo.