You should be using premium gas / 91+octane. New Mexico elevation is typically 5,000 ft +. Many gas companies lower octane levels as elevation rises. Chevron may have lower octane ratings for their premium. Suggest looking at pump to see what rating you are purchasing. Car needs 91+ regardless of altitude. If Chevron has reduced their octane rating, you may want to check other brands in your area. You have some gas companies in your area that used to sell 100+ octane gas.