Best Towing Gear Ratios - 96 K3500 CC Dually

[52weekbreak]

I have a beautiful all white 1996 K3500 Crew Cab Dually with a 7.4 Vortec and auto transmission I acquired from my Uncle who was the original owner. I pull a 33 foot fifth wheel trailer that weighs in at about 10,000 lbs fully loaded. The truck has 4.10 gears (GT5 according to the codes). The truck pulls great at 55 MPH (90 KPH) or at 75 MPH (120 KPH). In between these speeds, it is either gaining speed or losing speed or constantly in and out of overdrive.

At 60 MPH (100 KPH) the engine is turning over 2100 RPM so I am thinking that maybe I could use a lower gear ratio. This truck will never be good on fuel and I am not concerned about a slight increase and would appreciate the extra acceleration from stop.

Opinions on whether or not it would make sense to move to the HC4 4.56 gear ratio?

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[great white]

If you're not concerned with a bit of a hit in fuel mileage and higher rpm at highway speed, I see no reason not to.

10,000 is the max trailer weight for a 3500 with 4.10's so it might be worth your while to go up a ratio, seeing how you're at the rating limit. Won't do anything for the suspension/brakes/frame/etc, but it would likely make the truck less "strained" getting and keeping it moving.

A rough WAG with 30" tires, 4L80E in OD and 4.56's is 2400-2500 rpm at 65 mph....75 mph is going to drop you somewhere around 2700-2800 rpm.

6-8 mpg is a fair bet at those numbers and weight....that's older class 8 truck MPG territory.

 

[52weekbreak]

Thanks - Not afraid of a little more in gas (got over THAT a long time ago) but would like about an extra 300-400 RPM and a little more off the line. Now I have to source the different diff's for front and rear.

 

[52weekbreak]

Has anybody installed a Gear Vendors Under/Overdrive in their truck used for towing? I need some extra gears more than a gear reduction.