Jerry is right on the money about the reversed 4th and 5th shift position on the early roadrangers. Eaton made a bunch of the RT910 transmissions from the mid 60's on up to the early 80's that worked on the 250 to 300 horsepower diesels common back then. Final gear was direct 1 to 1 and not an overdrive. Overdrive could be achieved by switching the 4th and 5th gears on the countershaft. RT510 and RT610 transmissions were lighter 10-speed roadrangers suitable for the gas engine trucks with airbrakes. With a little practice they are all easy to shift without the clutch
