Better to have too much power than just barely enough. I know it hurts on the gas mileage but if you don't have to use the truck as your primary vehicle then that extra power is nice. The money saved in gas won't be that significant over the year. For example:

At $3 per gallon using a truck 8,000 miles 20mpg vrs 15mpg equals: $1200 vrs $1600.

Consider the wear on an engine that is just managing to pull your boat, not to mention the stress as you struggle to accelerate into traffic and the $400 per year becomes less meaningful. If you want a big boat you need a big truck.