Poor fuel consumption X5 diesel

[514.X5]

Hi

I have been getting poor fuel consumption on my 2011 35d X5. it struggles to stay under 10L/100km. ı mostly do highway and cruise at 100km/h most of the time. I know she can do better than that sure.

-Replaced the thermostat that was staying open.
-Did a DPF delete and tune, I really thought that would help but was not noticeable.
-Did a carbon cleanup 2 weeks ago that eliminates carbon build on diesel/gas engines. No positive results.
-Air filter is clean.

What else could I check or what worked for you?

Thanks