2011 Ram 3/4 T Cummins crew short box, 185K Miles. Just returned from a trip from NW Minnesota to Alaska, 7606 Miles through all terrain types from flat farmland to the mountains. Towed my Ranger on a steel trailer for the whole trip. Averaged 14.1 round trip. I get 17-20 on the interstate @73 mph, empty, depending on wind.
I deleted my truck at 100K miles after the Cummins warranty expired. The only reason for do so is that the O2 sensors kept going out and throwing a code and the CEL light would come on. Every single time I called the dealer, (30 miles away) I was told that the O2 sensors were on national backorder. I finally got tired of the run around and did the delete. I used a Motorops tuner, set on "light tow", and all is good now.
As far as starting goes, I don't bother plugging in the block heater until we get sustained well below zero weather. For us in this part of the country, that usually means about 2 weeks in late January - early February. I have the block heater on a timer and it comes on for 2-3 hours in the morning before I leave. Starts right up.
Hope this helps.
MNBill