As you know I purchased a 2001 Chevy 2500HD with 26,000 miles. It has the 8100 V8. Ran the first tank through and was glad to see that it got 11.6 m.p.g. Of the 320 miles only 40 were interstate most was city driving and some was pulling a trailer. A good mix. Will update when I pull a trailer for an entire week. (Next Summer LOL) as I still use my 227,000 mile Chevy Z71 daily.