Heath in light of the tow weight and distances, plus plans for the Cape I would go the diesel. And go an auto for better performance in the sand. Only problem I have myself going diesel is some diesel soot accumulating over the bow of the boat on long distance runs - polishes out easily though and if you have a boat cover or industrial glad wrap for long journeys it wouldn't' be a problem. I have a manual myself as I much prefer to drive them nad like the control, but sand performance suffers. WRT driving around town auto wins again, and both will be thirsty but hey you can't have everything!