BNSF 3664 and BNSF 3665 are making their first revenue trip over Colorado's Joint Line as they pull 17,700 tons of Engle Butte Mine coal. These ET44ACH are BNSF's new six-axle Tier IV locomotives. Unlike the previous four traction motor ES44C4 and ET44C4, these motors have six traction motors. Being extra eight tons heavier (218 tons) than other AC traction locomotives, these "heavies" in theory can pull better than other modern locomotives. As a result, management made this train into a "test train". The test was to see if a the coal train can still pull the hill with the second motor isolated. The power configuration was 1x2. The 1.4% ruling grade of the northern slope of the Palmer Divide proved to be more than what three "heavies" can handle. Nearing the top of the 7,200' summit, the heavy coal train stalled out. Even after putting the second motor online, the train could not start up. This resulted in the train having to back down to Spruce and get a running start at the summit. It was discovered that reason the train may have stalled was due to the locomotives running out of sand. Here, with all four motors online, the 17,700 train crest the summit of Palmer Lake and begins the down hill run towards Monument and Colorado Springs.