^ That comparison above although blurry, is comparing diesels to the 1/2 ton gas engines and not always the biggest gas engine.
Narrow the gap a little more..... and the fuel mileage numbers are skewed at best, complete bs at worst. I've driven or owned 3/4 of those engines and anytime a V8 gasser is getting within 1 mpg of a diesel of the same vintage, one of them is lying about the mileage.
The newer 1/2 tons are closing the empty mpg gap, since about 2010, but only if you run the little oe highway tires and live by 65 saves lives!
Fact.....that chart was developed by someone who is trying to prove gassers are cheaper.