My only experience has been with the Ford 460 with the E40D three speed overdrive transmission. I DO know that towing in overdrive and locked in cruise control is NOT the most efficient technique over all. I prefer to try to hit a balance between lugging down the engine, burning up the transmission, constantly up and down shifting and wondering when the beast will explode at 4k+ revs. I do this best by controlling the throttle myself. I may get up and down a hill a little slower but, if I can avoid a few shifts, I can save fuel.
I'm sitting in Ninilchik, Alaska as I write this and have Burned nearly $3500 in gas getting here. I'm almost at the halfway point of my trip so I have approx. $3500 more to go. Believe me, I'm trying to save all I can... Having a ball.......