I agree with Spastic Dove, the slower ones are harder to catch. For me I always run up over the top of them and drop my elbow and forget to follow through. I seem to rope tougher with tougher cattle!
The video didn't play well on my computer and was hard to see, but one suggestion, when you pull your slack when your heading pull down like your going to slap your thigh. It looked as though you pulled your slack upwards like your heeling, you will pull your loop off. But again it was hard to see the video, if I'm out of line I'm sorry. Roping is probably the most frustrating, rewarding hobby/work ever!!! I feel for ya!