Christian, I can only take a guess here, but maybe its to heavy. Hickory is a very dense wood, and with 2 shots of lead it might be "deadening" the action.
Personally, the first thing I would try is a lighter wood, say poplar, and just a single shot, or even better like a yellow pine w/ no shot. It is difficult to get those kinds of weights (2-3oz) on a mambo style lure, where distance is the objective. I haven't tried though, I know youll figure it out.
Another thought is to make a larger lip to give more action, or even cupping it.
Keep trying
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