With a scanner hooked up to my 97 ram reading live data and cruise set on 70 MPH on a straight leval road with no wind, it needs a higher throttle angle to maintain 70 in direct than it does in OD, also the overhead console instant readout goes up 3 or 4 mpg when switching the OD on and back down when you turn it off. Also since it is only useing 25% throttle to maintain 70 in OD I bet it could handle even higher gears and get a little better MPG, I am confidant returns would diminish but still be there.