I have always lived at high altitude. Right now we live at 8500 ft in the mountains. I have made lots of bread. I always use dry yeast that I buy by the pound and store it in the refrigerator. I increase the amount I use, use as warm as possible liquid (don'[t want to kill the yeast) and raise it as quickly as possible. I let it more than double before punching it down and shaping it. Again, I let it more than double. Bake at the highest temperature recommended. Be sure that your room temperature for the rising period is warm enough so the yeast multiplies quickly. I have put proofing bread dough in a slightly warm oven when necessary. Maybe some of this will be helpful to you.