How high are you when dropping the boosters? Probably all you need are some big fins at the back of your core. If it's too high for fins to be useful, add some vernors and engage RCS as you stage.
Another approach would be to make bigger side boosters and a smaller core stage, so that you drop the boosters higher where there are less aerodynamics in play.
That's my quick answer without looking at the craft file
My large station launches generally look like this: