Like I said, I haven't seen the video. When I think of overstriding, I think of front-side because that's where ground contact would be made. This sounds more like a postural concern rather than an overstriding concern if you're talking about excessive backside mechanics and anterior pelvis tilt. If these are the concerns, overstriding may be a problem, but only as a result of low heel recovery and pelvis tilt. Where does it look like the root of the problem is?