My first reaction would be you are over reaching before striking the ground - pointing the toes/foot and with your foot extended out in front of the knee. Try doing some fast running in place drills and notice how you naturally strike the ground. Then run forward and focus on striking the ground sooner, similar to where you strike the ground in place.
Remember that form should not change with speed, the only thing that changes is your distance per strike. Distance per stride is increased thru power provided into the ground with your stance leg to propel your forward.
The focus should be on this power to increase speed, not by reaching out in front of you to gain distance.
I am a good example of what Eric is referring to. When I started with Eric I very distinctly over strided. Reaching/pawing out with those toes, exaggerating a landing on the outer edge of my forefoot. I still have that tendency, but with focus and persistence and running in place before I take off it is becoming more natural for me to not reach, land with feet under me. My foot strike is more neutral as well. I also think the strength work has been key. My hips and gluts are stronger and my knee drive better, stronger/sustainable. I notice I start reaching when those muscles start to fatigue.