Yes, any diesel HD now-a-day will get 20 on the highway (minus the DPF and EGR crap).
You can't be serious with the MPG comparisons between an HD with a diesel and a half ton with an ecoboost. If so, then you're nuts. 15 MPG average on a new diesel is common. Ecoboost does better 100% of the time.
We ran two 2003 Dodge Cummins on our farm from 03-09. One Auto and one 6 speed. Auto got 14 mpg average, 6 speed got 15. I have run three 6.0 PSD's into the ground from 03 to 08 and averaged 15 to 16 doing the same work.
I assume you are talking HWY, and city miles combined? I seriously doubt Ecoboost does better 100% of the time. From my understanding Ecoboost MPG goes to total shit when you use the truck to do real truck stuff. Hell my moms 08 4WD Lariat crew can get 22 MPG on the highway.(At least according to it) IDK exactly what my dads 01 Ram 3500 4x4 diesel gets, but he has told me that he is been very impressed, and pleased with it's gas mileage. Most old 7.3 Powerstroke guys I've know have claimed to get some pretty nice MPG's with them also. Even the Duramax guys I know(severel) act like they get noticeably better gas mileage with their 3/4 ton than they do in their 1/2 tons. I've never personally owned a diesel so I can't talk from experience driving the trucks from day to day, but I have used them along side 1/2 trucks, and they always have gotten better gas mileage when towing. If Ecoboost truly only gets a extra MPG or two over the gas v8's then I can see a 3/4 diesel competing with or bettering it's MPG.