Hoosier,
I pour my lead into my baits,But here is what I would try.What everyone has said about shifting too much weight rearword is right..But..try drilling a 3/16th hole at the very back of the bait..Don't make it so deep it interfears with your rear hook hanger..and pour smoe lead in it.Some times a small amount of weight placed that far back can eliminate your tumbling without effecting the action too much..Nathan