Boxster Stamina

[kk2002s]

I am surprised to see the variations in MPG on the Hwy. I could only speculate 6 versus 5 speed. I have no mods so maybe mods reduce mpg??
My prep was new oil, air filter, clean the MAF. The plugs and belt only had a couple thousand miles on them.
My MPG is typical of what I'm use to
What I was alluding to in the title 'Stamina' was running the engine 14 hours in 90 degree temps at 3k rpm
Then thrashing it up and down those mountains 500+ miles.
Get back on the Hwy and the engine runs even more efficiently.
The original clutch (70k miles) never complained even when I got lazy and kept it in 3rd climbing at 3k rpms

I was very nervous that this car couldn't just run like that but I do like an adventure.
Probably why I bought a Boxster in the first place
I was picturing myself changing the AOS in the dark and rain, on a lonely mountain road, the engine still blazing hot and of course I wouldn't have any cell service