I own a 05 3500 ctd dually, 4sp auto, 4.10, with 3800 miles. Fuel mileage has averaged 11 to 13 in town and 12 to 14 on the highway (75 to 80), drops to 10 to 11 with the fifth wheel (12,000#) at around 60 to 65 highway. In other words it's almost as bad as the hemi 2500 I had before.

Question: will an overdrive unit bring fuel economy up (not to be used when towing the fifth wheel, just when I'm hauling air and rain water). Has anyone tried this yet?

 

You already have an overdrive. 4th gear is overdrive. Seems like you should be getting a little better mileage than that. My dad has the old 12 valve cummins 3500 dually 4sp auto with 4.10 gear and he gets 12 mpg pulling the camper in the mountains and around 16+ with no load. His truck stays in OD at all times. It says in his book not to take it out of overdrive unless pulling very big loads up hills.. The new cummins says just the opposite i believe. (i just bought an 06 2500 CTD last month) Mine has a 3.73 ratio and acts a lot more like a gas burner tranny than the diesels i've driven in the past. I'm not sure, but you may be able to have the ECU programmed with one of these programmers to make the torque converter lock up earlier.

 

Clemson, he's asking about a gear venders overdrive gear set.

will it help with economy, it might. it will bring the engine RPM down, but there are other ways to increase fuel economy.

my 04.5 also has 4.10's plus I have a manual. with 24,000 on the clock I can get 18-20 if I'm easy. towing a small trailer will drop that number to around 15-16 depending on load. a large trailer will put me around 12-14 again depending on load it could be lower.

with 3800 miles it sound about right, just give the engine some time to run and break in better and if you want better mileage without dropping over 3 g's look at a performance box that increases power. generaly on low settings any box will increase mileage from 2-4mpg and some times more.

 

What performance box are you talking about? On another note, I just came back from a car show that featured "Big Daddy" Don Garlits. It happens that he is towing the old swamp rat around in a large covered goose neck trailer (weight ?) with a 3500 dually. After putting on about 22,000 miles the fuel pump system failed (while in Atlanta). The only way they could get running that weekend was to replace it with a unit for a 2002 (non computer driven). Since then fuel economy is up 3-4 mpg and power increased as well. Any thoughts anybody??