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If its 52 cold, it may just be a regulator spring on the low side of tolerence. The adustable spring may fix it. While I've never done it, I understand its also possible to simply shim up the existing spring with small flat washers.



Agreed. Junky--if your cold PSI tops out at 52psi (same as your hot) then that's indicative of the pressure bypass valve in the pump opening up, and 52 is on the low side.
Simply take off the big nut at the back of the pump and find a washer or 2 that will fit inside the Nut/cap. That preloads the spring a little more and makes the valve (its a metal cylinder that uncovers a dump-port when under pressure) harder to move into the bypass position.
You will notice higher pressure.
I have done it, and in your case I think it will work.
Easy.