Keeping your shoulders square to the lane is very important. If you are trying to play straight up the boards and hit third board, stand a few steps back from the foul line and only use your push off and slide. Your arm should act as a pendulum and only swing front to back. Try the push off and slide while releasing at a particular mark. Once comfortable, do it throughout your entire approach.
I used to have a problem with tugging the ball inside my mark, but that was caused by 2 things. Bad timing and dropping my shoulder!! Make sure your shoulders are square!!
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"I am the most consistent bowler in my house....
I consistently SUCK!!"