I'm driving a 2017 Cascades with DD13 and DT-12 I can get 7.4MPG without even trying. It's a complete truck and they have no APU. We have the Optimized Idle system. The engine will start and run forfor heat or a/c and to recharge the batteries. I would say it runs about 5 hour every night maybe more. Plus it does parked Regen every 8 hour of idle time. So it normal won't Regen when stopping just for 10 hour break. When we do 34 hour reset we get 1 or 2 parked regens.
The DT-12 trasnmision take a little getting used to. Most driver want use engine brake like regular one. It's programed to always drop a gear and raise the engine RPMs to give you crazy strong engine bake. That messes up a lot of new driver because they are using it all the time and the truck seems out of control they always say.
It really made for hills, not every stop light or stop sign. Stage 1will Always keep engine RPM 1,200-1750. The same for stage 2 but strongrs. Stage 3 will ALWAYS keep RPMs 1750-2200. It keep engine RPMs high to give you crazy strong engine brake. So going downhill at 1750-2200 RPMs is normal. So obviously you don't use it in snow or ice.
It never gives up if truck slows down and you keep stage 3 engine brake when you hit 1700RPMs you should switch to stage 2. If not it will downshift and raise engine RPMs to 2200 and keep slowing down. That what I mean it never quites untill you turn it down or off. It will keep slowing truck down and keep dropping gears. It a cool feature because one you learn it you can go downhills without touching brakes. You can just switch from stage 3 to stage 2 and the transmission won't shift gears.
The DT-12 trasnmision also has a special downhill mode most people don't seem to understand. You can set the cruise control and lock the truck into a set speed like down to 30MPH and the transmission will hold that speed by switching engine brake from stage 1,2,3 automatic. It can hold a truck and trailer on like 8% hill at speed you set if for down to 30MPH.