There should not be any need to reprogram the ECM for the gear changes. My understanding is that the sensor is at the wheels, not the drive shaft, so any change to gearing is automatically accounted for.
Klenger, if what you say is true, then Morse's numbers show that he is getting approximately a 2% increase in gas mileage, under highspeed, highway driving conditions with the AT; EVEN if the ecm does not calculate accurately to real world driving (and I still don't understand why DC cannot get it right unless it's to fool the EPA) :-laf it should be good at least for relative readings. At an average of 20,000 miles driven per year, a 2% increase in mpg a person will recoup about 150 gallons per year (Did I DO that RIGHT??) which translates to $500 annually (Much more, of course, as the price of diesel goes up) In 5 years or less the swap out to 3. 42 differential gears will have payed for itself; ((Also assuming that I did the math correctly and Morse's #'s are indicative of an average improvement for anyone with a 3rd gen, and that nothing else on our trucks breaks because of the swap)). Furthermore, and perhaps more importantly, it will let anyone who wants to DRIVE highways a little faster and let our CTD do it closer to it's sweet spot at highway speeds. How this mod fairs for driving under various towing conditions with the AT remains to be seen, but with Morses' numbers, I am pretty sure this will be an excellent mod for all trucks with the G56 6speed, as obviously one can simply shift to adjust for load and terrain. And the G56, as MRFrost and others have pointed out, is simply geared to low for fast highway driving with the 3. 73's. Speaking of the G56, I have been rereading the old posts on this thread, and I can't tell if anyone with the 6speed is going to try this mod or if all of us G56 drivers are waiting for someone else to do it first?! #@$%!
I do know that based on Morses' #'s I would eventually like to do this mod, but it will for sure be AFTER the pac brake, the brake smart, the modified headlights, and probably even after the hydraulic winch; But it's always nice to plan ahead:-laf. Hell, now even CaptainMike might want to see what kind of mpg's he'll get with the 3. 42 at slower highway speed--I'd imagine payback might even be quicker, though of course still not near enough to buy a new Porsche. But what can you haul with a Porsche, except *ss?? Thanks to everyone for their ideas, experiments, insight and plain old hard work!! Please, someone check my math?!
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