Rebecca, my husband and I made that trip in September (well, over the mountain and on to the other side to Grand Junction), and we had to take oxygen along. He had done it the year before with no problem, but a trip to Wyoming in the spring had given him his first experience with air hunger, so we checked with his pulmonologist. The man was a marvel. He arranged for Matt to go into the hyperbaric chamber at Duke, where they set took him up to the altitudes we would encounter going through the pass and hunting on the Grand Mesa. Based on what we learned, he perscribed oxygen and educated me on when I would need to start giving it to him and how much. We made the trip (our last one, I'm afraid) safely.
Again, we'd don't it before with just the Trilogy, but things had progressed to the point that he couldn't handle the altitude without adding anywhere from 2 to 4 liters of 02, depending on altitude. Note that this is ALWAYS with the Trilogy.
Enjoy the trip and travel as much as you can while you can!
Becky