You are in Maine, not a lot of mountains there. Do you find yourself pulling large mountains when you travel?
If not, a gas engine should do you just fine. The GM 6.0 is in the 2500 and 3500 and is a fine engine. The Ford 6.2 is in the F250 and F350 and is also a fine engine. Ram is coming out with the 6.4 Hemi, but there isn't much real world experience with it. I would argue that any of these gassers would be just fine for those weights unless you are pulling serious weight up serious inclines in serious altitudes.
I would prefer a new gas to a used diesel as long as the gas engine is stout enough.