You have a timing chain, not a belt.
At 260k, it's probably shot. Most 3.1s seem to toss the chain around 175-200k, in my experience...
But that may not be your problem....I'd suggest spending $25 for a vacuum gauge, easily the best money you'll ever spend on a tool, and see what the reading tells you.
If something internal went away, you'll be able to determine that quickly. If the reading is solid, you can relax a bit, it's not critical, just gotta determine the cause from there...