I have had low pressure for quite awhile. I have replaced everything but the well pump. No water will go into new pressure tank. Pressure gauge goes to 20 lbs does not shut off well runs continuously. If the air pressure in tank is set at 28 lbs and the pump is only pumping 20 lbs then seems to reason why it want got in the tank. I’m guessing I need to pull my pump out?

If by replacing everything but the pump means you have changed the inlet pump filter then that's likely. The filter is the first thing to check or replace when you have low pressure conditions and it may even be an obstruction or bad check valve causing this problem.

Is this pump above ground or in the well? Your description sounds like it's in the well. If so, then how old is the pump? How far down is it?

The pressure in the tank has nothing to do with preventing water from entering. Worst case scenario is the pump is worn out and just can't deliver pressure. Could be leaking well pipe but that's unlikely.