This same problem happened to me when editing 'Boys are back in town' (it goes completely off-synch halfway through).
I suggest a more simple method - while still in preview, editing away, put the marker at certain points to make sure it's still in synch. When rendering, do a test first - low-res - to see if the general synching is fine. If it is, save a HQ version.
I always do this when editing, I'm kinda a perfectionist for trying to get the synching spot-on - even doing it frame by frame if it is required. Lengthy, but worth it.
Don't rush your editing, take your time and then witness the fruits of your labour. Oh, and hopefully the stunts will be no bad either