Neither does the gas engine, in fact it gets worse gas mileage than the diesel.
You may be spending slightly less per gallon but you'll not be getting as many miles per gallon either. Couple that with the depreciation hit (twice, assuming you bought the eco new) and it'll take you literally decades to recoup the difference.
I could give a **** if you just want a new truck I'm just pointing out that the idea that you're going to be saving money on gas is ludicrous.
I think he used the new math they teach in California. It works inside the state but not outside the state.