Chevrolet Repair: 1994 chevy 1500 p/up oil pressure problem, light flickers, distributor shaft

Question
I own a 1994 chevy 1500 cheyenne 4x4 p/up with a 5.7 liter engine. The truck has 110,000 miles on it and has never plowed. The truck recently had anintake gasket leak at the rear passenger side of the intake. The leak was a moderate one. The repair shop did the gasket replacement and suggested replacement of tune-up items that included spark plugs,plug wires,distributor cap and rotor, pcv, fuel and air filters. they also replaced the oil pressure sensor which was a quage type that sends signal to the instrument panel cluster. The sensor is located on the top of the intake towards the drivers side next to the distributor shaft. The truck was retimed. The truck appears to run fine, no loss of power or drivability issues. Heres the problem. The oil pressure at start up remains steady at 40 psi. As the engine temp increases the oil pressure slowly creeps downward. When the engine temp stabilizes the oil pressure needle is at 1 line above the low red warning marks on the gauge. When at idle the oil pressure needle dips slightly into the red and the check gauges light flickers on & off. When reving the engine the needle willmove up to about 20psi then settles back above the red marks. This oil pressure problem was never there until the intake gasket and tune-up jobs were done. The only other odd sympton would be that the engine seems to have a slightly louder sound and vibration to it than before? Any suggestions would be helpfull as I can get no solutions from where the truck was repaired?

Answer
Hello Robert,
First, check the oil, and see if there is coolant getting into it.
Then change the oil, making sure you use the same that you used before.

I would probably screw in a mechanical gauge, and see what the actual pressure is, and if it is good, I would replace that sensor again.
That one beside the distributor operates the fuel pump when oil pressure is present. It may also operate your gauge, but I 'm not positive. But it could be bad.
Before replacing it, make sure the ground wire from the right rear of the intake manifold to the firewall got reconnected, and there may be another black wire that connects to the same bolt, which could be a ground wire from that sender.

Van