Running pain...

[VeloVT]

piriformis syndrome?
http://www.rice.edu/~jenky/sports/piri.html

or maybe just tight hams/glutes???
how well do you stretch after each run? when you're putting in that many miles it becomes really important. one stretch that is really simple that I found helpful is as follows:
1. Lie on your back on the floor, with left leg extended on the floor.
2. Bring right knee up to your chest. Hold for a while, until the stretch starts to abate.
3. Take right ankle in left hand or crux of left elbow and pull up slightly (up=towards bellybutton/shoulders, not towards ceiling), at the same time using right hand to push right knee towards left foot. (Knee should still be bent, and ankle should be somewhere in the neighborhood of your left hipbone). Again, hold until you feel like you've gotten enough stretch.
4. Take right ankle in both hands and pull as far towards head as you can, keeping left leg extended flat on ground, and keeping right knee as straight as possible. Alternately, depending on your comfort/flexibility, you could take your ankle in your right hand and pull your right thigh down gently with your left hand, letting the right knee bend if it needs to.
5. Release and repeat on the other side. Repeat on both sides if it feels like it would help.

BTW I am not a PT, just a runner. I have trained for marathons before but haven't had the pain that you're describing -- but I have read about similar symptoms, FWIW.

Good luck!!!