As the engine will see more load during times of full throttle, it will experience more wear too during those times (but not the rest of the time), but it shouldnt be to any significant extent.

The MPG claims tend to be a bit excessive on most aftermarket chips anyone saying "up to" generally means "significantly less than"

I think you should do it, as there is no significant downside really and the extra power would be useful on hills im sure in quite a heavy vehicle like that.