on Ford's fuel estimates it says somewhere along the lines of "fuel consumption based on average driving habits"

I tend to go a tad slower if in not in a rush. plus I have a V6, dunno if you guys knew

 

I don't see how people can get 20's mpg. Granted i have 35in tires but I only get about 11-12 mpg (mostly city though) with a cold air intake and a programmer. At completely stock I still only got about 14 mpg mostly city once again.

 

It actually doesn't hurt to use the 4 by system in the rain, it actually helps it. If you only used it when it snowed or to go off road it would only get lubrication at those times, that is if you do it daily. I live in the northwest and it rains quite often here. I;ve done it quite often when I travel the highways. It helps you keep from hydroplaning in those large puddles that build up on the road. It also comes in handy when it is wet to leave a stoplight without spinning your tires. It is not good to use on dry pavement. When it rains it is like using oil with ball bearing there is less resistance. As for your different gas mileages they will all vary depending on the climate conditions (warm or cold). Wintertime is worst than summertime.