Well as far as the mpg ... I have no for sure way of telling ... as for the New diesels sucking ... I build 340 of them a freaking night and I know what they do .. And if your an engineer the DPF pipes suck and the threads on them need a pitch change !
Once you hit enough miles there is a burn off on the exhaust .. You are required to run at a consistent speed for 20 minutes, if you fail to do so the burn stops ... you have 3 chances to do this burn off before the computer puts you in a limp home mode and you are required to go to the dealership to have it "fixed" after 3 burn offs the cat is toast ! Thats coming for our engineers at the plant not something I'm pulling out of my ass. Yeah way to go new low sulfur diesel fuel