I think altitude plays a large part in this problem, I also believe being supercharged magnifies it.

I threw 3-5 cel's a day after we got out of the flat land, on the way to Moab.
No less than 4-5 a day while in Moab, & the same on the way home.
Since I've been back at "normal" altitude, no cel's at all.

Fortunately for my sanity , I can read & clear codes on the fly with my scan gauge. (from Tone)