You are measuring the draw down of the tank and you have a serious problem or the pump would not be running 7.5 minutes between cut-in and cut-out with no water being used. The problem could be many different things, such as blocked jet or water inlet, a suction or pressure leak, something wrong wit hteh pump itself, the wrong jet etc..
More likely you simply need to get rid of the filter cartridge and its housing. It could be blocked along with the water meter.
BTW, the watch and a bucket method of coming up with the output gpm of a pump is a poor way to do it and it is not accurate.
If you can't find the problems and you think it is the pump, you should ask Grainger what is wrong, and next time, buy from Bob at pumpsandtanks.com.