Have you ever had it serviced? I take my machine in once a year. when they pull off the back it is like felt in there from all the fabric dust we generate.
It might be the timing, although that is more likely to show as skipped stitches.
And it could be the foot pedal needs cleaned, I just heard from a friend that had to have that done.
Her's wasn't hesitating, it would continue to run the machine when she took her foot off.
Good luck!