Thats pretty impressive, maybe its time for me to switch? My 2011 335D which is JR Stage 2 tune with EGR delete doesn't do as well as your X5. My D averages about 27mpg around town with mostly highway driving around Houston. Best I've ever gotten is 32.5mpg on the highway driving to Wyoming. Worst I've seen is about 22mpg with no highway driving.

My D Lost in the trailer storage shed.
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My x5 4.8 best I've seen is 19.5 (more typical is about 17-18mpg) driving on i-10 at 80mph, and worst was 7.3mpg while towing my trailer out of east Texas at 65mph on hilly terrain.

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