Having been in your same situation, I also suggest you look at your load distribution (heavier items closer to your back, and lower in your pack as close to your centre of gravity as possible), and also look at the set-up of your webbing / belt kit... training for this particular course that you speak of, a tendency is to want to have as many pouches on as possible to increase carrying capacity. If you have too many, your main ammunition pouch / utility pouch will be to much to the front.

Especially on an uphill, the tendency to improve biomechanical efficiency is to lean forward, reducing propulsion needed and instead increasing leg lift to allow a controlled falling forward (ie - the POSE or chi running method). This then increases active insufficieny of the hipf flexors, combined with added resistance from the webbing, and altered COG is actually a very common cause of psoas overuse in the forces.

Hopefully no post means you've passed selection and am now on RIO... if not, pm me as an aussie with a background in your situation.