Just be careful with a single dog on a sled- the x-back harnesses put a whole lot of strain on the lower back- I can see it in your video. I'd recommend getting your dog a different harness like the wheel dog harness from man-mat or a harness from non-stop. It can make a big difference for our long-backed shepherds to take pressure off the lower back and hips.
Do you have give/bungy in your tug line to the sled? That can help too.
Your dog has super drive for the work though! Keep it up!