A video of you bowling would help in assessing your balance issues. Balance problems can come from a variety of issues. Timing is often a chief culprit, but being out of balance can also result from improper step cadence and spacing, excessive drift,too much (or too little)
vertical and /or lateral spinal tilt. If all of these check out ok, then being out of balance at the release often is the result of pulling the ball down (muscling) as the ball begins its descent from the top of the backswing at release. It is very, very important to let
gravity power the downswing. John Jowdy called this "waiting for the ball". Too often,
a bowler will anxiously pull down on the ball once their slide foot has arrived at the foul line, causing the bowler to rear up and step off with their trail foot in an effort to regain their balance. When your slide foot arrives at the line, just be patient and allow yourself to "wait" for gravity to bring the ball down. Once the ball has reached
your slide foot, then simply direct your follow through GENTLY outwards toward the
pins (breakpoint).
Good luck!