Yeah it depends on so many factors, at such a small difference it shouldn't matter.officially there is a 1 mpg difference between their ratings, real world is a toss up, depends on whose right foot...
I don't think its a complete decoupling though, there is always some parasitic loss from the front shafts IMO..It would matter if you were driving around in 4x4 drive all day. However the truck operates in 4x2 unless you tell it otherwise. Id say it sits a little heavyier due to extra components. Thats all.