I have been getting 20 to 22 mpg highway and with my 5th on 15 .Its only a 25footer and i can hardly tell its on there .Man I love this truck .I had a 6.5 before this for 10 years never had a problem did a few adds. thermestat high out put water pump and fan I never had it overheat and i live in some major mountians,I tow quite a bit flat deck trailers and my 5th but after reading about it here. I thought best to do the cooling mods. It was a good truck also when I sold it the buyer said what dosn't work on it ? It was a 94 and had a full load and I thought for a minute and realized every thing worked and had never given me a problem.It was a little slower up the hills than the dmax but a really good truck.If my 05 dmax treats me near as well I.ll be happy. And boy with the extra power and the heated seats I'm in heaven !