While mpg is important, no matter the vehicle from a Prius to a Peterbilt, it is the cost per mile that should be the primary focus.
For instance, the GM 6.2L Ecotec 3 in the 1500, while delivering some nice mpg numbers, according to GM manuals, it requires premium gas. Now lets do a little comparison. My 2015 2500HD 6.0L gets around 17-18 mpg on road trips, but averages around 14.5 for all miles. From other forums I frequent, the GM 6.2L in the 1500 has been getting around 22-23 averages for highway miles and 18-20 for overall averages. Would seem the 6.2L in the 1500 would be the better thing, right?
Well, Premium in my area has hovered around $3.20 a gallon recently. E10 regular hss been around $2.50. I use E15, which has been a dime less. So a 6.2L 1500, on premium, getting 18 mpg average, is costing about 17.8 cents a mile in fuel. The 6.0L L96 in my 2500HD, getting about 14.5 average, is costing about 16.5 cents a mile in fuel, using E15. Imagine, a much heavier 2500HD Z71 with beefier snow plow prep package is costing a penny less per mile to operate than a lighter 6.2L 1500. If the 1500 is getting 20 mpg average for all miles, it is almost a wash on fuel cost per mile compared to the heavy 2500. And my 2500 has 4.10 diff ratio which really makes the 6.0L grunt well, while the 6.2L has 3.42 (or 3.73 in the max package). With those taller ratios, the 6.2L can do better mpg.
I like better mpg as well as the next guy, but I am a business man, and I look at value for my dollar. I can out pull, out haul, etc any 1500 even with the hot 6.2L motor, and do it cheaper as well. No brainer. The 2015 2500HD 6.0L is sitting in my garage.
And the 6.2L Ecotec is a relatively new motor without a proven track record. We don't know yet how it will fare over extended periods of operation across the spectrum. The L96 6.0L in the 2500 has an extensive track record of longevity, durability, and reliability. And that factored into my decision as well.
I pulled on to the grain elevator scales last weekend with my 2500, two people, full of fuel (36 gallons), and about 200 lb of tools and such in the back. It weighed in at 7380 lb. I have been waiting with much anticipation, for someone to load up a 6.2L 1500 so that has a comparable gross weight, drive it around for their normal stuff for about 1000 miles, and then see what the mpg is. I have confidence that the mpg spreads I mentioned before would shrink considerably, and the best cost per mile value in using my 2500 would be even better.