Basically. I hooked up a pressure gauge to the front loader valve and I'm only getting 1,000 psi max at full throttle. My cs apparently came with just a belly mower and the po added the loader along with the backhoe later on in its life. I doubt anyone ever checked the relief setting after each was added. I also checked the pressure where the hydraulic lines for the backhoe attach and got the same reading. I'll change all filters before going at the relief valve and shims but I would like my guns loaded ahead of time is all.
The loader kit does not come with a different relief valve nor does it require that adjustments be made. The BH uses an optional Remote Hydraulic Valve, but it doesn't alter the pressure of the system. Have you confirmed the flow rate of the hydraulic pump? Have you confirmed that there are no air leaks in the system? It is strange that that your hydraulic system is working at 50% capacity - something is obviously very wrong.
When checking system pressure, it should be checked at the Pressure Check Port of the Hydraulic Power Lift (HPL) control valve, not the loader line. The hydraulic pump has a flow of 24.6 lmp (6.49 gpm). The Hydraulic Power Lift has a relief valve setting between 1,850 and 1,920 psi. The safety relief pressure is 2,560 psi. The priority is sent to the steering unit (7 lpm) with the remainder used for lifting/lowering.
The rebuild sequence of the relief valve can be found on page 10-50 of the shop manual. Unfortunately it does not provide a part number for the shim(s) but it does note that a .5mm (0.020 in shim will raise the pressure 20 kgf/cm3 (284 psi) and that a 0.1mm (0.004 in) shim will raise the pressure by 4 kgf/cm3 (57 psi). It would appear that you need three 0.5mm shims. If the shims do not produce the desired result, you may need a replacement HPL control valve. You could easily take one shim to a hardware store and try to source (nearly) identical washers. If they are unique, they can be found at McMaster-Carr. I would also carefully check the seal behind the spring for cracks or deformity. There is a note that the orientation of the seal (behind the shims and spring) must be inserted with the dish-out portion facing towards the spring and the flat side of the seal must face toward the poppet. Make sure that this hasn't be put in backwards.