Interesting data: I added one 45 degree PVC fitting on the tube going from the pump to filter housing. I wanted to stop the cooler lid from rubbing on the tube when I opened and closed it. From adding that one fitting my flow rate seems to have reduced a bit to just over 5GPM.
I also took this opportunity to add silicone sealant to both sides of by bulkhead rubber gasket. My bulkhead nut appears to have loosened up over time and I had a slow leak through the bulkhead gasket to the outside of the cooler. I would recommend adding silicon to your bulkhead gasket.
