I just did a run from Mission to Merritt BC (2016 SV with Auto Trans) via the infamous "highway thru hell" & after 222 kms the car calculated 5.2 L/100 kms. After fueling up in Merritt I used 12.78 Liters which I calculate @ 5.75 L/100 kms.
I should point out I used HWY 7 to Agassiz & then over to HWY1 & then the Coquihalla. I set the cruise @ 105 kms/hr (GPS read 100) as there was little mid week traffic and kept the speed no less than 90 on the big hills with the AC off.
On the way home I stayed on the freeway the whole way (250 kms) used the AC & still got an indicated 5.2 L/100kms. Usually I do better on the way home because of the long downhill sections back to the Coast, where the indicated usage is 0.00 L/100 kms with the wheels driving the engine, NOT Neutral.
I heard a story years ago in school about 2 guys in an Army jeep trying to go as fast as possible down a big hill
by putting the standard transmission in Neutral. The teacher called it "Mexican Overdrive".
Sounds like they hit a very high speed until somehow the transmission
accidentally popped/got bumped back into gear causing the flywheel to sheer off & fly through through the trans tunnel taking off the drivers leg!