You have a few options depending on which way you come into Colorado.
If you enter Colorado on I-70, then you can turn in Limon, and take 24 to Colorado Springs. Then take 115 to just outside Canon City. Take 50 West from there to Montrose.
The only section that is slow is from Canon City to Salida, which follows the Arkansas River in a canyon, and doesn't have much passing. Traffic should be lighter that far South though, compared to roads leaving Denver.
If you're coming in on I-76, I would recommend I-70 from Denver to Grand Junction, then 550 South to Montrose.