Let's get one thing straight...I have no vested financial interest in what I am about to tell you...this is just from me to you, something that has been an advantage in my training and racing.
Get on the Chi Running program.
I bought the book a couple of years ago, and have been focused on the "Chi stance" every since. It takes concentration to change one's running form over time, but this was a good thing to pursue.
I had, for many years, run hunched over at the waist, which put my body into a less than efficient mode. Chi Running teaches you to position your core in balance with the legs, upper chest and head, and then lean forward at the ankles to let gravity pull the body forward.
It's subtle, but it works.
Keeping focused on Chi stance allowed me to run a negative split on the last of four loops at the Jacksonville 50K last year...even when tired, the stance lets the body remain efficient.
Give Chi a chance, you may find some new game in your racing efforts.