Chasing problems and niw this? - 2000 Sierra

[Blue'72]

Hi friends, I guess it's been a few years, but anything I've needed help with thus far has been answered by searching this great site.

So I bought a used Silverado, GMC actually, to replace my Dodge RAM that didn't fit the Bill because of it being, a Dodge RAM.. Well my 225k mile new truck needed a fuel reg and iac motor for starters. It ran great until it started randomly misfiring, but ran good most of the time.

Took it for a dump run and it was running bad with the cel flashing the majority of the trip. Came home, parked in the driveway and moved the wife's car out of the way so I could get it in the garage, but the truck wouldn't restart when I was ready to pull it in. Finally got it running enough to pull it in before it died, and then replaced the fuel filter. Tried restarting it and it sounded like an old cheapie rebuilt starter trying to start an old sbc but kept catching and grinding. Still wouldn't start and I thought the pump was bad, even though the old filter was plugged.. Starter still sounded bad.. Last night I determined that the pump was good, and today I removed plugs and they were all covered with fuel. Turned it over without plugs and starter locked up. Finally realized that the short tab on the starter was broke off, so I went and got a new starter. The motor sounds horrible when it runs now. Luke something mettalic is rattling around in it. Drained some oil and it's clean. Checked the inspection hole in bellhousing and behind the plastic cover for starter, and everything looks fine. I'm at a loss because it doesn't sound like a rod, but wondering if a valve dropped??

I'm sorry for the long read. But if anyone has any ideas, I'd like to hear them. Btw, I did remove the socket and ratchet from the harmonic balancer...I'll try posting a video of it. I can't stand to run it mire than about a second because it's that horrid..