From looking at the video you posted it seems most of your arm speed is spent at the beginning of the pull, you're pulling directly into your left pec, and you are stalling your momentum with a pause from your right foot landing and your left foot pushing off.
From what I've learned is that to maximize your effort the beginning pull should be generated by your lower body and your arm should be driving the elbow forward and the disc to your RIGHT pec/bicep. Imagine trying to pull through where your right shoulder was during your reach back.
The acceleration should then start from kicking off with your bag leg. This drives your hips and torso while all you have to do is extend your arm and tighten your grip. Plus a lot of disc speed can be generated from actively extending your wrist at the moment up to the disc releasing.
If you're near Richardson I'd be happy to go throw with you.