1994 Dakota 5.2 with 5 speed manual transmission

Tachometer seems to be reading at least double what the engine is actually RPMing at. Example: The engine is running about 2,000 rpm the tachometer is reading 4,000ish and then sometimes the tachometer is just acting all sorts of wacky bouncing around.

What is the way to go about diagnosing this kind of issue? Cluster? Some type of sensor? Thanks