One of many diesel vs gas threads on here......hen e still my at top.
But with this in mind.....if I were OP I would get a ne GM with the 6 so granny, an additional 60 or so ponies, I would find that to be cheaper over all, than the iirc about $6-7k or so for a diesel. You can.buy a lot of fuel for that difference. You will not be that much slower other than at elevations of 7000' or above. How often are you that high?
This is from one finding a sb 350 doing fine pulling what my dmax pulled a bit faster, but not enough.to write home about it. Would trade this truck in on an equal 6.0/6 so granny with 4.10 gears.
Marty