Another thought after what Marnold said.

BC, go over to Mark Wein's lesson site also, and he has a lot of free lessons on rhythm and picking in time. The reason I suggest this is that along with digging in to deep, another thing that will hamper what you are trying to do is not having your down stroke and up stroke in time. It is easy and natural to have your down stroke over power your up stroke so that the up stroke lags just a touch, or some other like symptom. I struggle with that one myself.

The series of lessons on rhythm starts with basic clapping, and goes up through 16th notes I think. It is worth starting at the beginning and working the lessons through. Very helpful.