Funny you should ask this question. I just purchased a 0-3000psi gauge to check the pressure on my tc33d. I'm not happy with the loader power and I've been looking at the manual and it says, if you have the single spool valve kit, the pressure should be 2130 + or - 70 psi when connected to the diverter valve. It also says that if you have a "double - spool remote control valve", the pressure should be 1750 psi at the high pressure tube while moving the control lever to the lift position. It sound like the 1750 number is comparable to your reading. I don't know the reason for the different pressures readings. Both test should be done with fluids warm and tractor engine running at full throttle.
I didn't answer your question about the maximum safe pressure because I'm looking for the same answer. If I don't get an answer, I'll raise the pressure 10% over specs. They should have a built in safety factor much greater than that.
Regarding your question about how to increase the pressure: the diverter valve is located on the lower, rear, right side of the engine where the lines to the loader control valve originate. On the bottom of the valve there is a plug and as you remove the plug you will fin shims that push against a spring. By adding to the shim thickness by .004 inches, you will increase the pressure by 51lbs. As for the loader valve pressure adjustment: you should find an adjustment screw with a lock nut attached to it. This should be located on the top of the valve housing next to the the spools that the handle is attached to. Turning this in should increase the pressure on the reliefe valve, in turn increasing the output pressure.