hmmm... well yeah 4x4 vs 2wd is worth a few mpg loss, and the wide and heavy wheels/tires are probably worth 1 or 2 mpg loss. If you're supposed to get 19 hwy and getting 13 I guess that's not far off... I put heavier tires on my truck and seems like around town I get the same mpg but hwy has decreased slightly, maybe 1 mpg. I almost always avg 17-18mpg, before the tires it was more like 18.
Breathing in and out is good enough for me.