I drive a 2016 Eco and avg 27-28 MPG for mostly highway driving. Mph is 65-70. I tried cheaper Def and dropped to 25-26 MPG and went back to Peak Blue. I have a K&N air filter, but haven't seen a difference in MPG since I installed it about 3-4 months ago. I'm very happy with mine. I change the oil every 6,000 miles and rotate the tires. It's been very reliable.
I just got back from a 1,654 mi trip to WV, Pigeon Forge TN, and East Asheville/Sugar Pine NC. Lowest mileage I saw when towing my 5,700 lb 24ft travel trailer was 13.5. While on the Camp Creek WV to Pigeon Forge leg, I had the check engine light come on. I took it to a RAM dealer (Rocky Top) right in the area of I-40 & State Rt 66 near Sevierville TN. (They were GREAT! They squeezed me in and it took about 1 hour!) They read the codes and saw: 1) Over fueling condition and, 2) Low voltage condition. They cleared the codes and told me while they had it, they were going to overwrite the computer with the NEW program without the 8 "cheat codes". I still saw a low of 13.5 towing. I will report back to see if I have any changes in my over the road and local usage. Was getting as high as 28.7 on a long trip and 19 - 23 around town (some interstate Hwy travel back and forth to work for the higher numbers). Stay tuned.....(Mine is still stock!! Hahah) Speaking of stock tune, I can't wait till the lease is up and I buy her out. With the stock tune, I was pulling up a 5% grade for about 2 miles (I-64 WB near Sandstone Mountain) had throttle to the floor, in 5th gear, she would not climb past 55-56 mph, was spinning about 3,600 rpm. Saw coolant temps near 230 and oil temps near 260. She cooled right back down after that pull and she is still together!! I think she is a "keeper"!Sounds about right. Slow down to about 65-68 like me and hit 24ish. With the gde tune I hit 27-29. 70+ kills the mileage crazy fast. Mine is a 4x4.I have a 2015 Ram 1500 ecodiesel with 34,000 miles. 1.55 gear ratio and full size topper. 90 percent of my driving is interstate and about 25 percent of that is pulling a 3,000 lb trailer. I have never once gotten over 21 mpg. Usually average 18 to 19 mpg with out trailer and 12 - 14 with trailer. After having topper installed mileage dropped about 1 mpg to the current 18 - 19 mpg. Never had a code or any other problems. Generally drive 75 - 78 mph.
Anyone have any idea what might be going on? I've bought fuel in at least 10 different states so know fuel isn't the problem. Hope this is not a cam timing gear slip issue.