Similar situation to the OP, in that our truck is predominately a daily driver. But it did need to be able to tow our 2011 31.5 RLDS six to eight times a year. We ordered a 2015 RAM 2500 "Big Horn" long bed configured with the 6.4L engine, 4.10 rear end, bed camera, 5th wheel prep package, and creature comfort packages for the Mrs. I added a backup cameras to the truck and RV after we took delivery.
Truck arrived first week of June and we have done three RV trips with it so far. Cant begin to tell you how pleased we are with the overall performance. MPG has been hanging around 14 to 14.5 as a daily driver and 8-9 when towing, which are figures well within our expectations. The tow prep package makes hitch removal a snap when I need an uncluttered bed for hauling.
I had to chuckle at the so called "test" up the big hill where the RAM 6.4 was a bit slower. Other than chest pounding bragging rights for the other brands, it was of no value to me. In the real world of towing in combined conditions, we get to where we are going in the time frame we planned. My racing days have passed long ago, so arrival times are now planned using only the big hand on the clock.
Ok, thats my 2 cents on the RAM with a 6.4. Happy with ours an no regrets on the purchase.