My 4.3 powered 1500 got between 18-20 mpg with mixed driving, the best I got was 23 all highway. If you want a v8 15-16mpg is attainable with light/highway driving or even better, depending on what you've got.
If you wan't a consistent 20mpg or so, you should consider a ford ranger or possibly even a colorado. Since you only have a little boat a v6 ranger or s10 would work nicely, maybe even a blazer or explorer if you need the interior space.
Toyota would be the last manufacturer I'd be looking at right now, but thats just me.
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