Oil pressure guage gone crazy

I have a 91 Silverado, 350 v8, 5 speed manual,club cab 2 wheel drive. Had the speedometer rebuilt about 2 months ago all was well until now. I got a light on dash that said check guages. Oil pressure was zero. I took the oil sending unit out hooked a oil pressure guage directly in, oil pressure is good. Thought the sending unit was bad so I replaced. I started to drive to test and noticed light back on. Set the emergency brake,killed the engine, restarted and light was out, oil pressure back to normal. Released brake check guages light come back on. Thought I had short so started tracing wires, didn't find anything. Got back in vehicle and noticed the oil pressure guage at 60 engine not running. When I start the truck guage climbs like the guage is now up to what would be 90 if it went that high. Kill the engine it drops back to 60. I'm not sure if guage is bad or what now. Check guages light no longer comes on, but still lights in check status. All other guages seem to be working correctly. Thanks in advance for any advice.