The only way to get "more" is to raise the pressure on the Relief Valve. Have you checked your pressure to see if you are set at factory specs? You just need a proper guage and a hose and adaptors. Once you know what it is, you will know how to proceed. It is up to you if you want to exceed factory specs, but if it is below spec right now, I would have no problem in raising it.
here is your parts list below.
3000 PSI 2.5" LF LM GAUGE
3/8 X 1/4 NPTF COUPLER
3/8" X 12" 3/8 NPTM X 3/8 NPTM 3000 PSI HYD HOSE
1/2 NPTM TO 3/8 NPTF ADAPTER
http://www.
surpluscenter.com/Hydraulics/Hydraulic-Quick-Couplers/Quick-Coupler-Male-Tips/1-2-NPT-COUPLER-MALE-TIP-S71-4-928-AA.axd