http://youtube.com/watch?v=75UFbtNlmYgPrevious owner of our bus told me over the Christmas Holiday he cranked it up to 80mph driving east from CA back in the early 70s. 55 mph is 2900rpm(direct drive Spicer 4 spd) on the 401M. I don't even want to know what rpm 80mph was. He had to shut it down and let it cool after he sucked the radiator hoses shut. 55 mph with the new Allison 1000 is 2200rpm in overdrive. Theres north of 450k on this engine and it still has 145-150psi in all cylinders. First rotation goes right to 95psi. Spark plugs and exhaust pipe are medium ashy gray. No smoke and uses about 1/2 qt per 1000 miles. No equal to this engine. One tough *****. Youtube link not working for some reason. just type 1947 Allison into the Youtube search window.