My six doesn't get near that. I'd have to know more to tell you one way or another. Are they the same truck?
curb weight, tire, alignment, gearing, lift, how many inches of vaccuum they are drawing... I mean there is a lot more to this than "my friend has one that gets better mpg than I do, so therefore that motor is better than mine."
My ag teacher in HS had nothing but 460's and he was getting over 12 mpg with a box built over the bed hauling produce home from pittsburgh twice a week for his grocery store.