Help! Ford (F150) has got me totally confused

Thanks to all that have replied. The Ford build your own page is what is getting me confused. I want the supercrew w/5.5' box. When I select that and then select ecoboost it tells me I have to change from a 3.73 axle to a 3.15 axle at an extra cost of $2095. If I accept the change and then change to a 3.73 it's another $2270 but at least I'm where I want to be. It looks like the max payload package is not available with the 5.5' box which is why I couldn't find it. I guess the main question I have now is if we really want the 3.73 gears. I don't think we would ever get a trailer weighing more than ~7k lbs and less than 10% of our driving would be pulling a trailer. We do live in the northwest and most of our travel involves pulling through mountains, sometimes very large mountains but from the sounds of it the eb has ample power to handle just about anything.