i have a 2010 cummins automatic. is it better to just leave it in drive with the tow/haul mode on or shift it manually? if shifting manually is better at what rpm should i shift up

 

I just put her in drive. Sometimes I will lock out 6th if I'm going slow but that's it.

 

I tend to leave mine shift by itself, enabling the tow/haul mode both when I'm towing and when I want the more aggressive downshifts and raised shift points that it provides. As you drive with tow/haul enabled you'll begin to "feel" how modulating the throttle will control how aggressively the turbo "brakes" you when decelerating.
There are times when climbing hills that the programmed shift point leave you lugging a bit. Then I manually shift down a gear. I think that you can do whichever you want...shift yourself or let the computer handle it...and there is no right or wrong. The only wrong would be to allow the transmission to hunt back and forth between gears while working it under load.
For normal running around town type driving, I always manually bump down to 5th, and sometimes 4th, so that the rpms stay in the 1700-2000 range. According to the Cummins site, that's where you realize the best performance/fuel mileage and it keeps the engine from lugging and vibrating the whole truck. I also think that the higher rpms makes the regen cycle work better.

 

I tow a 5er in the camping season and I have done the deletes. I now find the Tow/Haul mode to aggressive in city driving and on flat terrain. I normally start off in T/H and then turn it off. I will leave the exhaust brake on and shift from 4 gear to 5th or 6th gear as required. I do this to keep the EGT'S around 1000F.
I have even down shifted in the mountains when towing uphill from 6th gear to 5th gear to speed up the engine RPM's. Thus to increase the Turbo air flow to lower the EGT temperatures. I do not like to run in the 1300 to 1450 F degree range in the EGT's now that I have deleted.
So to answer your question, I would drive your truck with the trailer attached and see what is best for you. Try to turn off T/H mode in the city and when on flat terrain. See how the truck and trailer response to this. If required then run T/H mode, your choice.
Jim

 

This is pretty much what I do as well regarding the EGT's.

 

I tow a 14,000+ LB 5th wheel. Towing I put turn on the E brake, tow haul mode and let the computer do it's thing. Hilly country I'll put it in 5th and forget about it.

Normal driving I just start her, put her in D and if conditions aren't slippery put the EB on and go.

As far as EGT these 6.7 are built to run hot, heck even the 2005 and up 5.9's were built to run 1450* for sustained times. Heat is a good thing for these 6.7's with their emission equipement.

Just the other day I was reading about a guy who put some thing like 250,000 miles on his truck in a short period of time towing. Cummins contacted the guy and gave him a new engine so they could tear his down and examine the inards. Everything was almost as factory new.

Moral is, put it in T/H, EB on and tow. The more you work this 6.7 the better she runs.

Have fun with your new truck, she's a pulling machine.

 

I generally "lock out" 5th & 6th gears (let the truck shift on it's own 1 through 4) then manually shift into 5th then 6th when I choose.