jet pump only builds pressure to 20#

My water pressure is low and with the pressure control differential it drops to nearly zero before the pump restarts. If I try to set the control to a higher setting, it will run forever. I don't understand why it builds quickly to 20 but can't go higher? Please advise !?!?
More information: It has two pipes to the well. It doesn't lose pressure on its own. (I have to use the water to get the pressure to drop and recycle the pump.) I dropped the pressure with the power off and checked the pressure tank, and it has 19# in it. I believe the well is about 75 feet deep.

It sounds like the jet nozzle in the jet assembly at the bottom of the well is clogged.

Is that a automatic wellman job or could I (a fair hanyman) do it myself?
Thanks.

Two pipes full of water and 75' deep, it is probably a 2 or 3 man job, but you can do it if you really want to.

Thanks, I guess I better wait for warmer weather though. It will be below zero here for the next several days.
Thanks again.