When I watch Moreno run he just seems to stop or almost stop everytime the first defender gets near him. I think it's a big part of him stumbling all the time, because he's trying to start/stop too much. It's so frustrating how long it takes him to accelerate. A lot of those negative / no gain runs, if he'd quit stopping at the point of attack, he could get a few yards and if the guy misses the tackle, he's at a higher speed to break away for a longer run.
When he runs hard, stops dancing, and finishes runs, you can see the talent that got him drafted in the first round. He just doesn't flash it much at all.