5 Raw minutes of pacing UP 4014 through Echo Canyon

I am at a loss for We paced a Big Q A QHow fast were they going, What was your speed A3540 MPH (56KPH64KPH) QDid you have a shotgun mic on your camera ABelieve it or not I didn t I shot this with my phone of of things QI see that the A (Front) engine on Big Boy leads the B engine by about 40 60 degrees at the start of the video. At the end of the video, both engines are in phase. What is causing this (slip or a slight average rolling radius difference Any ideas AFrom u