yes/no, it is overdrive at 0.65. Torque multiplication in an automatic only helps start up. Torque multiplication adds lift off the line but 0.65 is 0.65 once rolling on the interstate.
The reason/logic for 1:1 in medium, heavy trucks is 1:1, direct drive is the most efficient way to transmit power when fully loaded. And in trucks, it is all about putting the horsepower and torque to its most efficient use. 1:1, Direct goes straight, direct thru the transmissions top shaft, bypassing the power loss of gears and turning the lower shaft...... which is why heavy truck transmissions were never synchronized. The synchros also steal power.
ps the only reason for automatics today in heavy trucks is a shortage of drivers and a lack of time to train them..... the lack of clutches in light trucks is due to EPA and CAFE regulations. Todays computers can shift any vehicle at the perfect moment, delivering lower emissions and higher gas mileage than even the best most conscientious driver is capable of..... this might also be influencing the commercial driver market but ultimately in the medium/heavy truck market the issue is training drivers.
pps, generally in the medium/heavy truck market a truck with an OD transmission will also have a lower rear end ratio.
Five axle interstate trucks in the USA often have double overdrive transmissions and they fly when running under 100%.
We bought a deck truck from the USA, double overdrive 7 speed it also has a wheel lift. It can move 2 cars across state incredibly fast. I've chickened out driving it at 90mph..... I cannot imagine doing 100mph in a deck truck with a car on the deck and a car being towed. Overlanding I doubt we ever max out a medium truck. The smart way to buy a truck is to gear it for economical/efficient running at...... 60??? mph..... taking into account your final vision including GVWR and tire size.
Stock ambulances tend to be great choices cuz we often end up close to the factory ambulance weight and they tend to be geared for 70-80mph. Kind of an all around sweet spot..... unless you add larger tires effectively adding OD.... in which case a commercial transport truck geared for 65mph might be a smarter choice.
