F3s on Tennessee Pass By Angela Cotey | December 19, 2016 | Last updated on January 6, 2021 Email Newsletter Get the newest photos, videos, stories, and more from Trains.com brands. Sign-up for email today! Get Updates Rio Grande F3 diesels grind upgrade at Mitchell, Colo., a mile east of the summit of Tennessee Pass, in October 1947. Two steam helpers provide assistance on the 3-percent grade. L. O. Merrill photo Comments+ You must login to submit a comment