What truck

Hello everybody I have been in trucking for over 30 yrs mostly at the other end of the truck (dock) it is something I have wanted to do since I was 18 I've had alot of my relatives that were truckers and now I am starting my own trucking business and becoming an owner operator. My question is fuel mileage on the 387 Petes and Freightshakers Columbia and one more I here is getting alot of ridicule is the Volvo 780 with a cummins in it. I am strongly thinking of the ultra shift in all 3. So any advice especially if you have one of these trucks will be greatly appreciated.
Thanks bluesman55