rpm when towing

Industrial diesels seldom - never run over 2000 rpm but that has nothing to do with the engine in your truck. Your truck needs to be running between about 2300 rpm and 3000 rpm to be making peak hp with the Aisin. If you've got your foot to the floor, your in 5th gear and below 2300 rpm you should manually downshift.The 68rfe needs to be in the 2400 - 2950 rpm range to make maximum use of your truck's power. Basically if your foot is to the floor you want to be above 2300 rpm in 5th to make use of your engines power and above 2100 in 4th, otherwise manually downshift.

Flat ground towing medium/light weight don't worry much. You could manually shift to fifth and see how your mpg is affected. Your Cummins can run way above 2000 up hills for long periods. Cummins generators powering hospitals and Important facilities often run closer to 3k Rpms when necessary.

So running in TH will change gears automatically and downshift for me?

My gasser ran about 3500 going uphill. So 2000 for a diesel is not a problem going uphill. I dont think I could get it to 2000 on straight ground.
When cruising at 60 it is so quiet, I dont want to lug if, but don't know how to tell

If you have either auto, it will downshift when it can't hold the gear whether you have it in tow/haul or not.
Presuming you have a G56 then. Pulling a hill at 60 with 3.42s and a trailer in tow would be right about the time I'd downshift.
With 3.73s and close to OE size tires and likely more power than your truck if its stock, I'm downshifting at 55-60 up hills under load.

Turtle n Peeps wrote:
Put the thing in TH and drive. Forget about shifting and trying to out guess a computer.

And if it is hunting between gears, then lock it in the lower one. I lock out 6 gear when towing a 16K 5th wheel. It will drop of 4th on mountain passes. RPM go to 2100-2200 if I remember correctly.

It is at 1750 at just over 60.

Love it.

Chris

If you have the aisin tranny, then that is correct. 68rfe is different. There are hundreds of tranny rebuilds because of that thinking.

Put the thing in TH and drive. Forget about shifting and trying to out guess a computer.

If you have the 68rfe, it shifts really early, bogs down, and ends up working g the tranny very hard. Get some transmission tuning with EFI live to up your line pressure and shift points. Otherwise, don't let it go under 1400rpms or so if you are trying to accelerate or go up hills. Mechanically, I'd stay at 2000 done all day rather than be at 1400 when towing with 7k+ lbs. The 5th and 6th gear part of the tranny goes first, and hitting it down making power doesn't help it.