How should I adjust tire pressure to/from mountains

Living in the Phoenix Metropolitan area, we have our tires set at 75 PSI rear and 65 PSI front. Never had an issue. As concerned, checking tire pressure when at high altitude, they ready the same.
Also light for "LOW PRESSURE" comes on in morning, but then goes off a short time later. This tells me that all is ok, just temp may play a part in the readings. I don't adjust while traveling but still continue with my walk around checks daily and when stopped for a break or fuel etc. Good Luck & Be Safe ! ! !