CHECK THE VOLTAGE AT THE PUMP IF YOU HAVE A GOOD FILTER AND 12 VOLTS AT THE PUMP, VERY GOOD CHANCE THE PUMP IS BAD , SHEAR LUCK IT WILL EVEN RUN AT 15 PSI, IT MUST MAINTAIN AT LEAST 28 LB,S TO RUN CORRECTLY , HI SIDE SHOULD BE UPWARDS OF 36 PSI, HAVE YOU HAD THE ALT CHECKED FOR OUTPUT IF THE SUPPLY VOLTAGE IS FALLING OFF THE PUMP SPD WILL DROP, AND OF COURSE THE PRESSURE , JERRY