My 6.0 is chugging diesel like it was gas. My 7.3 didnt suck this much down. It will chug most of the time and seem really fuel efficient some times. I dont drive it hard, im usually at no higher than 2k rpm. I have a 4'' turbo back exhaust from MBRP and a air filter delete so Its breathing like a champ but im not seeing any gain in MPG, on the contrary.