Is it common for them to die or work erratically?

What controls them?

Reason for asking, I'm noticing how my truck runs in relation to the tach.

When the tach is basically flat line or off in la-la land, the truck seems sluggish, almost like I'm riding with the e-brake on.

If the tach is working somewhat correctly, the truck has snap, and accelerates quickly.

Am I imagining things or is there a correlation between the two?