Advice for quad cramping during run

I finished my first Olympic tri this yesterday (wahoooo!) and all in all it was a good race. My swim and bike were about where expected but the run absolutely killed me. Both quads cramped up with the first mile and never would loosen up despite walking through the first few water stops and then resuming at a slower pace. Each time the run interval got a little shorter before having to walk. Literally two charlie-horses for the whole run. That really sucked. After all the training it was pretty disappointing to post 10:25 mi pace. I generally train at about 8:30 which I can sustain over 9 mi or so. I did my bricks (3-4) although shorter than race distance and thought I was adequately hydrated. Plenty of water before, 24-30 oz gatorade on bike, water during the run.

Did I go too hard early, not train enough, not get enough salt, fluid, nutrition?

Can someone give me some advice because this is my third event (2 sprints prior) and I have yet to finish with even a decent run. I gotta figure it out. Thanks!