I have a 5000 PSI, 4 GPM, 20 hp Honda, belt drive cold water unit. The Mi-T-M CWC-5004-1MGH. I am interested in upgrading the pump to 6-8 gpm. Can anyone tell me where I can go to get the best pump and technical help replacing it. Is there a chart that can tell me for each gpm I increase, what is the decrease in PSI?