1999 2500 2wd 5.9l 24v, 410 rear end, 47re, Banks 4" exhaust. Took my first decent road trip since purchasing a couple months ago. 300+ miles each way towing 3500lb travel trailer, traveled from 1500 ft above sea level to over 7,000 with 6+% grades, some several miles long. Averaged about 65 MPH entire trip, even up grades. Would love to hear your thoughts on these stats. MPG going up - just under 13; MPG unloaded- about 20.5, MPG coming back - about 14 (all hand calcs, not lie-o-meter). EGT averaged 800 - 1,000 (occasionally close to 1100 on steep grades - 500 - 600 on down grades). Now for the $64,000 question - since this seems to be a common point of discussion: Would you have made this trip with O/D on or off? Thanks for your insights

 

On flat ground, OD. On grades, OD off.

Other than that, sounds good to me.

 

3500 pound trailer? I'd probably have left OD on unless it was hunting for gears.

 

Thanks for your input. I actually left OD on the entire trip, except for when I was in stop and go traffic and on one uphill grade when the traffic came to a crawl in front of me. Other than that, OD on. It cruised up all hills without downshifting. My understanding of when to turn OD off is if it is searching for gears and shifting around. Sounds like this may be true. Otherwise, with OD off I'm turning about 2500 RPM at 55 MPH. I'd be winding it out - probably close to red line - if I tried to run at 65 with it off. With it on I run about 2100 at 65.

 

I agree with the OD off only if its hunting for gears. I regularly pull our 6000lb trailer across the praries with OD on and get fairly good mileage doing so. As you mentioned, RPMs at 120kmph are too high with OD off and I'd be pissing through fuel. The point of OD off is to save your tranny.