I have a well that won't shut off. It gets t 30psi but will not go any higher. I have checked the foot valve, installed a new check valve and drained and pressurized the tank. When I pressurize the tank using a compressor, the pump shuts off at 40 psi and holds pressure. So there are not any leaks. Any Ideas? Could the pump be going bad

The only thing left here that wasn't mentioned was the flo control switch where the contacts start and shut the well pump off.

Was that also checked?

How to Find & Adjust the Water Pump Pressure Control - private pump and well system do-it-yourself repairs

"When I pressurize the tank using a compressor, the pump shuts off at 40 psi and holds pressure."

With all due respect, I think that would settle the issue of whether the switch is working. At any rate, the switch would not prevent the pump from continuing to run and yet not getting above 30#. It does sound like a pump issue.

I might add that a falling water table could account for this. However, that wouldn't really "zero in" on the 30# mark every time. A leak in the suction side could also do it, but your "holding pressure" test (which was a good idea!) seems to rule that out, along with the fact that you do not mention that the pump is losing prime.

The pressure switch could be one of the problems .

The jet or injector inside the pump could have debris in it.

I take it this is a jet pump? Shallow well or deep well?

It is a deep well, about 45 feet.