I know this is an older model F150, but this is kind of proof that you can make an economic full size half ton. This one has a Cummins 4BT (4 cylinder) turbo diesel and the owner says he averages about 30mpg. It also has around the same amount of power that the famous 300ci (4.9L) Inline 6 had, which everyone loves.
This was done with a much older body style which is less aerodynamic (and maybe even heavier) F250. There is absolutely NO reason why they can't get the MPG's and power they need out of these trucks with a similar setup as this, only brand new (possibly doing even better). Just an example of really where I personally think the base model trucks should be headed.