The fuel burn numbers on their engine diagrams are assuming that you are using maximum available horsepower at any given rpms. Your actual propeller power curve is at much lower horsepower than the maximum except at wide open throttle (assuming your prop is correctly sized). Adding in the alternator (65 amps is approximately 1.4-1.5 hp depending on alternator efficiency and drive losses). Pulling the dinghy might add as much as .5 hp, so figure and extra 0.1 gph for alternator and dinghy. That still leaves you around 0.75-0.8 gph. This all assumes that your prop is properly sized and is operating at reasonable efficiency. A dirty prop or a bit of seaweed on the prop can dramatically reduce its efficiency which will increase your fuel burn.

1 gph says that you are using about 20 hp to drive your boat at 6 knots. That is high for your LWL and displacement.

The fuel burn numbers for my engine are based on logged engine hours under power and measured fuel consumption. I log all engine runs (duration and rpms) and also all fuel fills.