I think the 1800 psi at 2600rpm may be for comparison sake only.
I broke out my TC33D repair manual and here is what is says:
FRONT (DOUBLE SPOOL) REMOTE VALVE
1. Install a 0-207 bar (0-3000 PSI) pressure gauge to the high-pressure tube, 1. <font color="blue"> (top hyd connection) </font>
2. Start the engine and operate the hydraulic system to warm the hydraulic fluid to normal operating temperature.
3.Set the throttle at full throttle. <font color="blue"> (2800rpm) </font>
4. Move the control lever to lift control-raising position and observe pressure indication on the gauge. Pressure should be 121 bar (1750 psi).
5.If required, adjust the relief valve by loosening the locknut and turning the adjusting screw, refer to items 15 and 16, Figure 8-76.
My additions are in blue.