Regarding the altitude changes, I am familiar with cars tuned to sea level that have some trouble with performance when driven up to a higher altitude - for the reasons noted: air fuel ratio. I'm wondering if an engine is perceived to behave better going top down versus bottom up?
I would add that tire pressures can be equally finicky when changing altitude. I recall a road trip: leaving Chicago and heading to Colorado. After driving in the mountains for a few days, the center of the tire tread was worn thin because the tires were severely over inflated once in the thinner atmosphere. I would assume there is a relationship here...
