last night out of no where I was driving home and happened to look at the dash and seen that my rpm tach was fluctuating anywhere from 0 to over the 6000 rpm mark. then rpm's of the engine are not actually rising and falling at all just the meter is acting crazy. even when car is off it sits at 3000. what would be causing this issue cause I am lost. since this started last night I feel like my truck is shifting funny could that being messed up throw off my truck shifting properly or am I just overlooking into it?

 

Plug in a scanner, and see what the PCM thinks engine RPM is doing. If that is correct, likely just the cluster itself having issues.

 

on the old Plymouth Turismo's and Omni's the computer would often go bad to cause tach issues.