2001 Chevrolet Silverado First Bought Truck Oil Pressure Ran Between 40 50 Now

WHEN I FIRST BOUGHT MY TRUCK THE OIL PRESSURE RAN BETWEEN 40 AND 50 NOW I HERE A SMALL KNOCK IN THE ENGINE AND THE PRESSURE JUMPS ANYWHERE FROM 40 TO 80. SOMETIME IT SETTLES DOWN AROUND 75 SOMETIMES 40 .THINKING A ROD WAS GOING BAD OR SOMIN ELSE I TOOK IT TO A LOCAL SHOP AND THEY TOLD ME THAT A SENSOR WAS BAD AND PUT SOME STUFF IN IT TO CLEAN THE VALVES BUT IT STILL DOES THE SAME THING DO I NEED TO TAKE THIS TO AN ENGINE SPECIALIST OR WHAT CAN IT BE. ALSO IT DOES HAVE A RADIORTOR FLUID LEAK SOMEWHERE IN THE ENGINE NOT SURE IF THIS IS RELATED

THX
DARRELL