I had the same problem. Changing my finger pitches (more reverse), along with some very good tips from Bill Hall who once told me that at the release point to make sure to "be nice" to the ball (along with creating a nice flat spot with the follow through) made a huge improvement . It wasn't easy. I started bowling over 50 years ago. My mentor in those days , an accomplished bowler in his own right, advised that when it came to developing a good follow through, told me to imagine reaching for the TV antenna
that was perched atop the roof of the center. In addition, all of us had a lot of forward finger pitch in those days, along with stretched spans and perhaps too much reverse thumb pitch--- all in an effort to gain that one extra, elusive "rev".
Time have indeed, certainly changed.