About as many opinions as members here lol!
Fact is, new Hemi dually will not have that much less power than your LB7, IF it's still bone stock. If your truck is tuned, it'll blow the doors off the Hemi, loaded. And empty too.
Stability and payload will be a huge bump for the dually but you know this after 10 years with a little truck under a big camper.
Fuel mileage.....guessing you pull 12-13 mpg Avg with the camper and boat.
Unless the 6.4 hemi is magical compared to every other newer gasser hd truck I have seat time in, you'll be able to subtract several mpg and add a couple thousand rpms to the equation going to the gasser over the Dmax.
It will be more than suitable for what you're planning. It will not be easy on fuel and won't blow your hair back as much as any newer diesel.
Think about fuel prices for your AK trip and how many miles you intend to put on it. That may help in the decision.
As well, there is a reason it is a "screamin deal". See any screamin deals on diesels recently? Me neither.
Decision is do you want power or lower price of admission?