I have the 3.73's in mine. If i could do it over again, i would have the exact same truck except with the 4.10's due to the increased tow limit. I don't think that either one will cost more in fuel as i get about the same as skidooman93 stated above.
Most trucks will have the 3.73 as they are standard. The 4.10's are optional.
I went from a 09 GMC 2500HD with the 6.0 to an 08 GMC 2500HD with the duramax to this truck and i haven't looked back. This best suited my needs and can do much more than i require of it.
Good luck and enjoy.
