Well, that might mean a stretched timing chain (timing gets off when you are coasting) but if it's drive-able and running well, that can wait until the next build.
For some reason these chains stretch within 50,000-60,000 miles. (spec is 5/16 inch, or less) When ever I re-build them I always use a double roller chain, end of the problem.
All that being said, it could be a number of things, distributor advance springs, or....it's really hard to tune from a keyboard.....= )