If you use wheels with the same offset as the original and tires with the same diameter there won't be any additional strain, but because of the low profile tires required the ride will be harsh and you will be at high risk of damage to the wheels/tires on rough roads.
Im thinking of running a 40 series tire so would that be better than the usual 35 series, and would the weight of the wheels put a strain on the engine/drivetrain driving the long distances?
Anytime you put heavier rims / tires on this truck it will strain it more. That strain will manifest in your gas mileage.
It's hard to say if any damage will be done but you can count on your wallet taking more of a beating. Many people run large rims and tires here so hopefully others will join in. I run 20"s in the summer and the stock 18's with heavy Duratracs in the winter. Mileage for me is 13 summer setup, 10 winter setup.
Not sure you would strain anything. But a harsh ride will be for sure and maybe a bit more rotating mass may make your brakes feel a bit weak. You can always fill up that gap with some BIG brakes!
I'm running 22's with 305/40/22. Nexen roadian hp. These tires are very very good for dry and wet conditions. You would probably do better with a 275, 285 or 290 with a 40 for a smoother ride.