I dont think a 550 will cary 5 ton. The single axle would not hold up.
Military trucks are rated for off road tonnage and will carry double its rated capacity on road. The New consumer trucks are not, like the F550 even a 4x4 model is only 6000 pound conventional load rated.
They are not the same and therefore can not be compaired. As far as size? A deuce is quite a bit bigger than a pick up truck.
Being payed by the mile means the slower you go and the more you stop, the less you get paid per hour. So I dont get how taking longer does not matter. Makes no sense?
As far as a Canadian gallon and a US gallon, two trucks exactly the same with the same tank, one in the US and one in Canada- No matter how you measure it they hold the same amount. Your gallon may be larger but costs more than a US gallon. So your truck is getting crappy mileage just like ours. Heck I could say my tank is one gallon and it will go 300 miles on a tank! Does'nt matter how you measure it, they like gas.