At 70 miles my gage usually reads between 50 & 60, but after I drive for awhile it drops between 20 & 30 and I get a knock on the drivers side of the engine. Could this be caused by sludge clogging the oil pump screen.
oil pressure on 1999 Chevrolet Silverado 1500
I would not drive your Chevy until a shop looks at this. You could ruin your engine if the oil pressure is incorrect for any reason.