Ive got a 1995 Chevy 1500 4x4, My stock gauge is jumping around. when its cold it reads around 60psi. after driving for a while it will read about 20psi. when i stop at a stop sign the engine idles down to around 500 rpm and the stock gauge reads 0psi but there is no knocking or rattling at all. Could this be My sending unit? Any other ideas on problems i could have?

 

Yes it could. Does the needle move around with the ignition on but motor not running? Try disconnecting the electrical plug to the sending unit (with ignition off). This should cause the gauge to go down to 0. Plug it back in (with the ignition off) and then turn ignition on but don't crank the motor and see what it does.

A properly working gauge should read 0 when ignition is off or on (when motor isn't running). If the needle moves around during these times then most often the gauge is bad.

This is obviously a late comment on your original post.........Please let us know what you did to correct the problem. Thanks!