If you did the test right....... then just under 22gph is what I get for 1qt in 41 seconds.

I assume you tapped into the system from the line that feeds the carb, installed a valve on the end of the line, turn on the pump and close down the valve to achieve 6psi system pressure.
Then time the flow.

I would try it at 5, 4, 3 psi as well, just to see how low the system pressure would have to be to flow the fuel you need (50-55gph).

My experience has been that when flowing the entire system, while maintaining the required system pressure....... you need something like a 140gph pump....... for your power level(600-650hp).

I have seen many systems not pass this test when fuel pumps that are marginally suitable are used.

The question now is, is it the pump...... or a restriction in the line/system?

Did you see what the free flow was?

I know of one instance where the free low was more than adequate, but when tested at 6si, there was barely a dribble coming through(about 6mins to fill a gallon can).