Homestake Pass out of Butte, MT is 6375'. Bozeman Pass out of Bozeman, MT is 5760'. Those will be the highest altitudes on your route. Both are fairly short going up and long descents. The city of Butte has been used as a high altitude training center for Olympic skaters Altitude in town is right at 5500' so may not be a good choice for a stay with COPD. Bozeman is right at 4700'. Once you come down Bozeman Pass altitude continues dropping until it is at about 3000' in Billings. You should have no problem towing with your rig. Just slow it down on the descents. Have a great trip.
