I do have a loader, and I know it has its own adjustable relief valve. I'll verify its operating pressure after the main lift hydraulics are checked.
With the age and hours on the tractor, I think it's not imprudent to check. I've read a lot of stories of pressures shipping 20%or more over time due to the springs taking a set.
I do not intend to "crank it up" needlessly, but I'd like to make sure it's set to factory specs (1920 to 1991 psi, if I recall correctly from memory)
Start with the easy thing to check, disconnect a loader line to lift arms or bucket. Hopefully you have quick connects.
Connect pressure gauge to the output from the loader valve. Activate loader valve sending pressure to new gauge.
Read quickly so as to not force too much oil through the relief valve(s).
If this pressure reading is OK, then there is nothing more to do.
Further, know that your pressure gauge has built in inaccuracy's. Typically +/5% of full scale of the gauge. A 3,000 psi gauge can be off by + or - 150 psi.
Adjusting a relief valve to read 1,991 psi is just fooling yourself as a normally priced pressure gauge cannot read pressure levels that accurately.
Dave