Main pump pressure should be about 2750 to 2800 or there about, i would not exceed 3000 psi though.
Like was suggested, T into the main line coming out of the hydraulic valve with a 5000 psi guage. Rev up the engine to max rpms and slowly pull the lift lever. after the mast tops out Watch the guage and see what pressure is. If it looks like it will exceed the 3000 psi mark stop and check the relief valve on the first section (inlet section) where the lift spool is located.
It will look like a cartridge valve with a cap on it, remove the cap, loosen the lock nut on the adjusting stem to make any needed pressure adjustments.
Loosen to lower pressure, tighten to increase it. Once you reach the desired pressure lock the locknut down and reinstall the cap.
If the pressure does not change when adjusting the the relief valve is damaged and should be replaced (not repaired).