Return line from the pump to the tank could be too small, and unless you are making over 700 HP, you don't need -8's to the carb. -6's would be plenty. You could be blowing the needles ( what size are they )off the seats periodically. How much does it creep? Magnafuel makes one of the best regs out there so I think you need to start looking somewhere else. High volume pumps usually require a return line from the reg - whether they have a bypass built in or not. Where are your gauges located in the system?