I think you should look into including a training program that incorporates weighted sprints and resistance running. This can be as simple as running with a weighted vest on, doing interval sprints while carrying a weight, or running/sprinting while pulling a sled or a friend/training partner pulls you back by a cable.
You can also intersperse weighted/resistance sprint days with long distance weighted running or running on a course that has a lot of high inclines.
Best of luck.