The Ram Powertrain Integration Manager explained to me that the Cummins 6. 7 is happy and efficient from 1200-2000 rpm. He said it would be better to tow at 1800-2000 than to downshift and get 2500 rpm.
That's interesting info. I'd sure like to talk with him. Not only that, but I wish he'd talk with whoever does the PowerSpec program, because it doesn't seem to me they're on the same page. It says, in their gearing guidelines for vehicles under 10,000 lbs. under GVW and vehicles in the 10,000-30,000 GVW range, that:
1. Recommended RPM range at target cruise speed: 1900-2400 RPM
2. Recommended RPM at cruise speed for best Fuel Economy or Economy/Power Balance: 2150 RPM
3. Engine speeds of less than 1900 RPM at cruise speed or 1600 RPM at 55 MPH should be avoided
In some respects, they're similar, but there's no justification whatsoever in the recommendations for pulling any kind of a load at any rpm under 1900 (unless it were at 55 mph, when 1600 is ok?). It's puzzled me greatly for a long time, especially the 2150 best fuel economy statement, so much so that I had to just decide they don't even know themselves what's best. (Try getting their recommendations to jive with any axle ratio other than 4. 10, for example - unless you tow heavy at over 80 mph, you're breaking the rules. Of course, towing heavy at over 80 mph is breaking some other rules, too, and I think they're probably more important... )
Attention: TDR Forum Junkies 
