I have a 2000 Tundra, 4.7l V8, 4x4, 220k miles. I can't track down the cause of this issue and I need some help.

When I turn the key, it starts right away. It revs up to about 1800-2000 rpm, then drops to a very low and very rough idle. It will die after 5-10 seconds. I can keep it running with the gas pedal and it seems to clear up and run smoothly when I get up to 2500-3000 rpm. When I try to hold it steady at 2000 rpm or less, it coughs and sputters and backfires through the intake.

This happened suddenly, not gradually over time. There are no check engine lights. So far, I've cleaned and inspected the throttle body, inspected the MAF (it's in pristine condition), cleaned the PCV valve, replaced all 8 spark plugs, and pulled the upstream O2 sensors to check if the cats were clogged (no change). I've also checked all of the vacuum lines for cracks, they all seat tightly and have no visible issues.

I've searched for quite a while but can't find a conclusive answer - what am I missing? What causes these issues?

Thanks