madhat

You can always get a gear vendors overdrive unit. They are pricey, but it'll put you where you want it.

Spooler

You won't regret the 4.10 decision. Towing heavy with an auto, 4.10's all the way. Interstate driving in the mountains it won't be shifting out of overdrive all the time to keep the speed up and it will be easier on the tranny in the long run. Empty driving you will take a small hit but for overall performance there is no comparison.

Roarinbear

The reason I'm looking for this info. is I have a Chevy 2500HD w/ 3.73 and that is all GM offers. I was towing a 9800 lbs. TT and getting about 10-11 mpg. The new 5er on order is going to be about 14000 lbs. loaded. I know with the Chevy on hills, on the highway it would down shift, and be taching about 3000 rpm's. I went with the 4.10's and the new 6 speed automatic, figuring it wouldn't be laboring as much, but I don't want over kill either. I thick it may be early enough to make a change in the order if I choose to.

rfeiller

good choice

Spooler

You will be fine with the 4.10 gears. I have never had to shift out of OD. The only time I used 3rd in the mountains is when a junky Ford was in front and keep slowing down to around 40 MPH( buddy I was following). At that time, I said the heck with this, locked out OD, and passed him. It was a 7% grade and I was heavy....

CoastalDav

With the 68RFE with 4.10's the engine will turn just a little more than 200 rpms as compared with 3.73's and will be about 6-7 mph difference in the two gear ratio's at a given RPM in 6th gear. (1900 rpm 3.73=77mph, 4.10=70mph)

Personally, I think you got the right rear for what your going to be towing, with room to move up in weight if you want. If you follow the Cummins guidelines for gearing your truck for work (towing or hauling) you want to be at 2100-2300 rpms for best performance and fuel mileage at 65mph, max load. For the 4:10 that would be in 5th gear 68RFE at 2300 rpms.

http://www.powerspec.cummins.com/sit...ng/gearing.htm

choose ISB.

Put a engine monitor on the truck and you'll see the difference in EGT's and tranny temp running in 5th when towing as opposed to sixth at a lower rpm. Lower RPM is more engine load.

Dave

Roarinbear

Thanks guy's that's great. You made my day. Happy New Years!