Fellow at work suggested going to this site and running the numbers claimed it made world of difference on his 2005 CTD 2500, just ran the numbers for a stock 2006 2500 Ram 4x4 with automatic an got the following results:

Gearing Recommendation Summary based on inputs to the Gearing Calulator on http://www.powerspec.cummins.com/

Selected Gearing
=====================
Input |help| Intended Vehicle Speed mph 65
|help| Transmission Top Gear Ratio select 0.69
|help| Tire Size select revs/mile 658 (stock 265/70x17)
|help| rear axle Ratio select 3.73

Output |help| Engine RPM at 55 mph Checkpoint rpm 1552
|help| Engine RPM at 65 mph Intended Speed rpm 1835
|help| Engine RPM at 65 mph Checkpoint rpm 1835

Assessment - Not consistent with Cummins Recommendations
The selected gearing combination will result in an engine speed at the vehicle's intended operating speed and at 55 mph below Cummins recommendation. The gearing combination selected could result in driveability complaints and increase the operating time below top gear. Both situations can have a negative affect on fuel economy.

Vehicle Profile
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Engine ISB
Application Pick-up & Delivery
Gearing Recommendation Type Line Haul
Typical Gross Vehicle Weight (GVW) Under 10,000 lbs.
Percent time operating off-road or on soft surfaces < 10%
Percent time spent operating on Interstate highways > 90%
Intended Cruise Speed 65 mph
Gearing Desired Fuel Economy

Gearing Recommendations Guidelines

1. Select a gearing combination that will result in an engine speed of between 2100-2400 rpm at the vehicle's intended cruise speed (mph).
2. For maximum fuel economy or for vehicles operating 65 mph or faster, select a gearing combination that will result in an engine speed of approximately 2150 rpm at 65 mph checkpoint.
3. Gearing combinations that produce an engine speed less than 1900 rpm at the vehicle’s intended cruise speed (mph) should be avoided.
4. Note: ISB is not intended for weight over 50,000 lbs.

Comments? [sm=feedback.gif]

 

The gearing calculator contradicts it's self. I ran it useing an intended cruise speed of 75 mph. The resulting rpm of 2178 clearly falls within the recommended range of 2100-2400.

My experience in real world driving is also different. I get better fuel economy if i keep the rpm at 1900 or less. With heavy loads (15,000+) I turn the overdrive off. That put the 65mph cruise in the recommended rpm range and keeps the trans from shifting constantly.

 

what you have to look at is that is not the Dodge Cummins ISBe, what you are looking at is the straight Cummins ISB engine that has not had Dodge work it over.

the Cummins ISB is rated at 275hp and 675tq, the Dodge Cummins ISBe is 325hp and 610tq. the ISBe is makeing more HP at any given RPM over the standard ISB. that calculator doesnt work with these trucks, unless your running 4.10's or have an 05 with the G56.