How's it going, everyone? I've got a pesky issue with my engine idling rough, and I was hoping to pick some of your brains for a min.

About 4 years ago, I noticed I had a slightly bumpy idle. At the time, my engine idled at right around 700-750 rpms. So, I had a shop check it out, they told me it was probably the harmonic balancer, and we replaced that. Sure enough, you could see where the old one had become separated. So I drove away not thinking much about it.

Well, since then, it's been bugging the heck outta me trying to figure out why I can't get rid of this vibration. At this point, my engine is idling at about 550-600 rpms, and when it does, you can watch the belt tensioner jumping all around. As soon as you bump the idle up to 800 rpms, it smooths right out. I've done the following to try and fix the issue:

-3 harmonic balancers
-1 new crankshaft pulley (in case the old one was bent by some fluke)
-All new sparkplugs (AC Delco or Bosh-I don't remember for sure), wires (Accel), cap and rotor (AC Delco)
-Replaced all the injectors and fuel filter, as well as ran seafoam for a few tanks of gas(had misfire codes under load, and was thinking maybe one injector wasn't working right-causing the rough idle)
-New air filter (cause...who knows lol)
-Cleaned the Mass Airflow Sensor (again-cause who knows)
-New engine mounts (the old ones had separated)

So next...all I can think to try is replacing the timing chain. It's never been done, and i'm sitting at 160,000 miles. I've never replaced a timing chain, nor do I mind learning. But is there anything else I should be looking at that I have missed? Are there any brands of timing chains/gears that you guys recommend? Thanks for the help! I realize there's other threads on timing chains, but none of them seem to have tried as many things as I have before-hand. So thank you for your patience and time on responding to another pesky timing chain thread.