4K Train Stalling with Wheel Slips and Sand

Second wheel slip video: I set up next to this train to record it throttling up. I was very surprised when it stalled out, and the wheels started slipping. I think the reason it was so hard for this train to get moving was the second and third locomotives, it seemed like they were barely doing anything. 0:00- Throttling up 1:25- Close up of the wheels 2:05- Slowly moving forward 3:09- Second close up of the wheels 3:34- Finally moving again