How do you get mileage like that? My 2014 will do average of 22 at best and I mostly drive highway. If I am ONLY on open highway, I can get to MAYBE 25 tops. Never better.
What speeds are you driving??
With my 2012, set up the following: 5.0, Michelin 18", TP 38-39F 36-38R cold inflated, top tier non ethanol or low ethanol premium gas all the time, intake inserted intake valve cleaning every 10k, fuel system cleaning every 3K, smooth driving in Eco mode (not using adaptive cruise, too rough and rides brakes, if there is traffic), no wind or little wind based measurement used in numbers stated below, AC off whenever can, stock systems-no
mods, windows closed, occasional 6-10 length drafting, once per tank full throttle "clear out the lungs" acceleration through several gears, Mobile One Extended drain or Penzoil Ultra 5-20...
Rural highways, drive for biz, 29-33.5mpg. Speeds between 60-70.
Interstate driving 28-32.4, speeds up to 78mph (cutoff of Eco light in no headwind sonditions).
Metro driving. Mixed major roads, stop and go, occasional town interstate, 23-26mpg.
Measured manually. Display reads between .5 under actual mpg to .5 high reading.
Heavy 19" wheels Blizzaks, lower tire pressures, and extreme cold weather (poorer winter gas formulas) reduces by up to 3mpg across the board.
2015 5.0 Ultimate.. Same car situation, except tires reading live on display, NOT cold inflated, while moving up to 40 rear, 38 front.
No extreme winter conditions. Set it to economy each time starting.
Rural highways about 1mpg less than 2012
Interste highways about 1mpg less than 2012
In town up to 4mpg less...
The extra 500lbs makes huge difference. I suspect uber wide tires also are not as efficient as 2012. And the 2015 is not fully broken in yet (which I consider to be at 10-12k miles as broken in).
In 2012, By 8-9k miles between the intake valve cleaning (at 10k), it appears to me mileage is going down. Also, if fuel system is not cleaned about every 3-4k, my impression mileage starts to go down. Even with top tier gas. 2015 has had one fuel system clean. Seemed like it picked back up up to 1mpg it had lost.
I drive these for biz ends, in a routine, taking many routes repetitive. I use many of the same gas stations which run through premium quickly and it is fresh. I know differences between adding head or cross winds, rain affecting mileage. I repeat mileage results because of the biz unless travel patterns.
Hills will foil the mileage. Can affect the 2012 to the bottom of the range I listed. The 2015 can go down more than two mpg in hills. Likely because of the extra weight. Head/cross Winds seem to affect the 2015 a bit more. Dropping the mileage on highway into the 24-24.8 range if they are uber strong. Does not drop the mileage to this level in the 2012. I did get a couple sustained tailwinds (wind at the tail both going, then shifting to be tail wind coming back after a frontal passage) in the 2012. Crazy mileage average of 36.2, measured. Luck of the draw. More times, have had winds shift to be headwinds both directions.
Hope this helps identify any differences you might see that is causing your mileage results.
And most around here know my view about dumping the V8 for the less than 40lbs less weight complicated plumbing TT V6. Real world mileage will not beat the Tau. Especially if they would put cylinder deactivation on the TAU.