The marbles in a tin can sound is probably a stretched timing chain. It sounds to me like it may be time soon for an engine replacement. Unfortunately, you live in The People's Republic of California, so the normal advice to swap to something better is much harder for you than it is for many of us as there are far more laws governing swaps than in most other states. I would try to find an acceptable used engine first and not a rebuild as it is not worth the money to rebuild the 3.8. It will never be much better than it already is. If you have a decent amount of time before your next smog check, consider running the current engine until it dies, and take the time it has left as an opportunity to save up for a legal swap.
