Originally Posted by blkmagikca
I tow at just under 60mph - between 57 and 59 mph with cruise on.
The lead diesel mechanic at our local Dodge dealership is a long-time personal friend. His advice was don't mess with the engine - no chipping - as the additional torque will shorten the life of the 4-speed auto tranny. The truck is equipped with a transmission oil temp gauge, and it is pretty much steady at 140 degrees, but does rise some when in stop and go city traffic.
All in all it was a good purchase (makes up for all the times I screwed up).
That's a consistent number, then, and I thank you for the context. It is the highway speed I run as that is the "fastest" slow speed one can attain just
prior to the onset of aero resistance. (The resistance curve shoots skyward). Also, CUMMINS indicates best mpg when engine is at 1300-1500 rpm, so the closer we are, the better.
The CTD is one heckuva truck. Much the best vehicle I've ever owned. And, while I agree with your mechanic, depending on the model year, a CTD can have retarded engine timing. FYI, a SMARTY JR used on or one step up from default configuration "restores" engine timing without adding extra fuel (where the problems of transmission longevity arise). There is no free lunch, one is not, IMO, "free" to use the additional umph so much as letting the trans shift early as the engine rpm rises that much more quickly. IOW, that "the truck is quicker" is not quite to the point . . it is that the engine does not "hang" prior to a shift (if that makes sense). And there is a measured FE benefit of around 1-mpg for average
One does not have to a boy racer to use some tuners for effectiveness (where burning less fuel is rightly understood as "performance").
But I don't have on either. And for the same reasons as your mechanic cites (in principle: potential reduced component life). But I'm tempted since with a manual transmission I might achieve just that much more control. About $600 USD. A reduction of about .5/gl per 100-miles (22/gls per 10k miles) for my truck & use. But better quality shifts might make the long payout worthwhile.
Thanks again. That makes about an even dozen owners of CTD trucks with 28'-'34 (8k-11k) aero aluminum trailers (Avion, Airstream, Silver Streak) who achieve that fuel mileage while underway with otherwise stock trucks.