How long, generally, is a break-in period?

Well did it get better after some miles? Fuel economy get better?
Just took delivery and I'd say the exact same thing you did. It better get better and be like the older Cummins or time for something else

 

No it didn't. It might've ran a little better but as far as economy, forget it. 4.7 mpg was all the better I could do

 

Let that Cummins drop down to about 1100 before down shifting. Yes some Cummins have to get some miles on them before they start performing. That is if your boss hasn’t neutered it.

 

No actually you are way out of your torque range your using HP not torque let that engine work down low. Hell my 565 with a 18 and 3.25 pulls great at 1100 to 1200 rpm got to let them work in the power band.

 

No. Under 1500 the truck was useless. I tried it every which way, believe me. 1800 was the pulling RPM.

 

Yeah same here. Thanks for getting back. Seems downshift early and get up to 1650 to save face. No low end torque at all. What a disappointment. Mileage the same as old truck and now $45/week in DEF. Figured would get better mileage to cover the DEF

 

Weird, I let it lug on down and once it starts pulling it pulls good. These new engines will bog down then start pulling.
Nothing like the old engines. Have to be driven differently and no idling

 

Yeah that truck drank DEF. 230 gal fuel capacity and I'd have to get DEF Everytime I got fuel. In this Mack I'm in now I get DEF like once every 2 weeks

 

The MX13 I drove was like that, 1000-1500 it pulled like a beast, over 1500 there was nothing there. There's 2 X15 engines, the efficiency and performance. The X15E makes low end power, and the X15P has no low end, it makes peak HP at 1950 RPMs

 

Mine came alive at 50k. Buddy of mine said his opened up at 70k.