Hello I have looked at this forum a few times on past problems but now I need to ask for some help. My tachometer is reading but 1000rpm to low. ...

Hello
I have looked at this forum a few times on past problems but now I need to ask for some help.
My tachometer is reading but 1000rpm to low. The truck runs like it should but the gauge is off. At cruise it runs around 600-700 rpm and idles below 0. Tonight it cruised at 1000 rpms. I have been looking for an answer but I am not to sure what to do. I have found that guys will clean their throttle body and mass air flow sensor but my truck is running like it should so I do not think a cleaning will work. Could it be just a loose wire or a sensor is messing up? What about a new stepper motor or do I need a whole new cluster? The truck runs fine so this problem does not effect me much, I would just like to fix it someday.
Thank you for any advice.

2005 GMC Sierra Z71

I would start with replacing the stepper motors. There are a few good how to videos on youtube.