You're probably strongarming your drives. I've been throwing 250-275 for nearly 4 years. Just the other day I had a distance breakthrough. I realized that I was keeping the muscles in my arm and shoulder far, far too tense. After reading This
this intructional article, I tried something. I power gripped my driver, putting pressure with only my fingers, while the rest of my arm was completly limp. I then spun my hips and rotated my body. The rotational speed turned my arm into a sling. The disc ripped from my hand and I felt it, SNAP!
Anyways, I hope my story can help you find some snap. Maybe some of the other members can give you some more technical advice.