I'm expecting 7-8 mpg on flat ground, up the mountain, probably 4, yeah.
I don't think it will be significantly worse than I already get based on previous towing experiences.
My dads trailer fully loaded with sleds and gear weighs about what this one will weigh empty, and I got exactly the same mileage pulling that trailer as I did my old Mirage.
I would think this would probably be a little less than that with the same payload in it, so around 7-8 mpg. Not great, but it's still a whole hell of a lot cheaper than taking on a $1000 a month payment on a new truck then having to buy more expensive fuel for it on top of the payment.
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Doesn't really matter either way, the truck I have now is paid off, so its what I'm gonna be using to tow it with for the foreseeable future.