The 2012 Roush CleanTech Ford F-250 and Ford F-350 trucks offer two tank options—in-bed, 49-gal. or under-bed, 25-gal. They’re equipped with a 6.2-liter V8 Ford engine, for improved performance over the previous-generation 5.4-liter V8. When compared with gasoline, vehicles fueled by propane autogas produce 17% to 24% less greenhouse gases, 20% less nitrogen oxide, and up to 60% less carbon monoxide. Roush CleanTech. 800-597-6874.