I ski at altitudes of up to 3500 meters. I’ve found that the cartridge in my Animus Ping pump has a lot more bubbles at altitude. The insulin vial that I use to fill the cartridges, is under greater pressure due to the expansion of air in the cartridge. I suspect that some of this air makes its way into the insulin that’s in the vial.
Bottom line, keep a close eye on the air bubbles in the cartridges you use with your pump.
I’ve found my Dexcom to be accurate at high altitude.
I keep both the CGM and pump (along with the tubing) & BG meters very close to my body to avoid cold related problems. At low temperatures, above freezing, BG meters won’t work.
Good luck on your adventure. I envy you