Hey there!
Posterior chain work is NEVER a bad thing! If anything, I would venture to say that most people can't do too much of it! What kinds of things are you doing right now? What are your warmups like?
It sounds like you need to de-activate your quads/hip flexors and activate your glutes! Obviously foam-rolling your quads will do some of that, but what kinds of stretches are you doing?
My favs for hip extension:
the tried-and-true "triple threat" protocol from JC Santana (hip lifts, straight leg hip extensions, and leg curls with the ball)
any bridge variations for that matter!
suplex lift with superband
kettlebell swings and cleans - because in order to do them properly, you can't "squat"...you must use your hips!
a side-lying girly hip abduction movement i call the "hip hinge and raise" (which you can kinda get an idea of on one of my ehow.com articles -
http://www.ehow.com/how_453569 7_fix-those-weak-links.html
i also love miniband lateral and diagonal walks as well as monster walks
i could keep going but those are some good ones!

hope this helps!