For the 4th weekend I took my Fiero to Flagstaff and since it's been here the auto transmission will not downshift like it normally does and the power from the engine is lacking.
I reside in the Phoneix, AZ area ( elevation 1300ft ) and the performance is great. Flagstaff elevation is 7000 ft.
Could the change in elevation cause the shifting and loss of power issues?
Not sure about your shifting issue, but yes.....high elevations will sap your power and it will be very noticeable (just not as much oxygen in Flagstaff as in Phoenix). I'm from Denver (~5300 ft.) and now live in Dallas (~500 ft.) and the difference is huge.