DD 15 with Dt 12 auto wont pull in 12th.

I am driving a brand new Freightliner cascadia with a dd15 and dt 12. When I put it in CC at 70 it slows down to 68 or somewhere around that. It slows down to 65 or so going up an overpass and then speeds up to 70 only to kick in e coast and slow back down 68. Hills are a nightmare. It will slow down to 55 before it will downshift. It runs pretty good if I put it on manual and run it in 11th at 65. It pulls the hills fine. I am old or at least my right leg is and i need cc to drive.

It has been back to freightliner and they did nothing useful. It is supplied and maintained by Penske as a private fleet truck. My boss wants me to go 70. We do an out load deliver and then pick up and come back. We dont have extra time our window is 7 to 5.
How is the truck supposed to run. I read in the manual that the throttle is not going to be open when in cruise. . Is there some place I can find a description of what Detroit says it will do on the highway. it doesnt pull very well with an empty flatbed in cc.

 

The cruise and the truck are both set at 70. It cannot pull 70 on cruise and slows down to 68. It will slow down more with slight grade or some wind. If I set it at 65 it will run a steady speed. in 11th it will also pull the hill and only fall to 60 or so. The same hill when set at 70 it will fall to 55. It is set up so you have press on the accelerator going down the hill and you have to press on accelerator to start up the hill. Then you have to downshift manually to get up the hill. It is so inefficient that driving in 11th makes better time. I dont want an auto that requires my constant attention. I am not driving on mountains. these are small hills. Most would consider it flat land. The truck is great around cities and country roads.. I drive on a stretch a lot that is 32 miles of stop lights and this truck is great to do it without stress and roll many lights. It just gets useless once it goes into 12th. If it were set for fuel milage it would not try to pull hills in overdrive. It is using a lot of torque with little result.

 

Mine does the opposite. it powers down the top of the hill only to e coast till you start up the next. Thank you I used your post to find a description of how it is supposed to work. I will ask the techs about it.

 

I have been through the menus and cant find such a setting.