low water pressure

Just installed a new big box store 3/4 HP shallow well jet pump to replace my old 1/2 HP gould, which died. The unit has a 20/40 switch, so i had 18 psi in the pressure tank when i primed the pump but it never got above 20psi and so never shut off. Not being a plumber, i thought maybe i had it wrong and should have had 2 pounds less than the cutoff value, so i cranked the pressure tank up to 38 psi and the pressure went up to 40 and shut off. After using some water, the pump reached its 20psi cuton value and started cycling again but this time never got above 27psi. The well water is notoriously dirty at times (it clogs up the pressure switch every 2-3 months) so i'm wondering if it could have lowered my water pressure that quickly. I had rigged the system to first pass through a sediment filter but with that arrangement, water pressure never got above 10psi, and no water was delivered to the house (10ft. above pump level) so i disconnected the filter. Any suggestions?

The bladder should be precharged to 2 - 4 PSI less than the kick-in pressure. You probably have a suction side leak or the water is so dirty it plugged the jet.

You need to build a bank of filters, starting with perhaps 3 at 25 microns, then one 10 and perhaps a 5 or a 1, which will give your system a chance at life. filters fast online has good ones cheap and very cheap filter cartridges, about a $1.50 EACH.

Although filters on the suction end could be quite problematic. Perhaps a large 25 on suction and the smaller ones on outlet of the pump.

There is a filter leading into the house and it works fine. The filter i tried on the line from well to pump is the problem...the pump barely primed and the pressure never got above 5psi.

The suction filter may have a air release button which will let air in when running.