Sounds like the bow is not in tune.You can get away with it with field points because the arrow is so streamline. But when you put on broadheads due to the additional frontal material ie: blades, even the slightest wobble that ordinarily would not be noticed with a field point will bemuch more pronounced with the broadhead.This will send your arrowswhere you don't want them to go.

I think there is a good tuning guide on the Easton website. It's not too difficult or time consuming if you follow the steps, just give yourself an afternoon to do it and you should be ok.

Good luck.