You're probably right, the problem lies in the pump and it's most likely the Valves under the head. There is a 3-fingered reed valve (flat, flapper valve) on the top of the Valve Plate, most likely one of the "fingers" is cracked therefore causing it to pressurize only 50 PSI.

Is this the style valves you have? I've also attached a diagram for your reference.

If so, we do have a Repair Kit that includes a new-style valve plate with all related parts and instructions, part# is AB-9429999 which we sell for $24.95 + shipping.

Thanks!
- MTR

As for the Torx screw, it has Loctite on the threads so it can be difficult to remove. You can purchase one of those hand "hammer" accessories that you can put a bit in and hammer the end of it, this loosens the bit most of the time enough for you to simply unscrew it. A hardware store may have this or even a tool rental store. I would go this route if you can't remove it.

As for the intake Filter, this should have been included in the Kit, it's a new type of Filter and it's a round, black plastic Filter which threads directly into the side of the new Head. It should have been in the same box as the Kit, do you not have this?
- MTR