Yesterday, my 84 300D turbo started running a little rough from just off idle until the turbo spooled. Not enough to cause a real problem, but it persisted throughout the day and started to be a little rough at idle as well. It wasn't consistent; sometimes it would run rough, sometimes it would be fine. Sometimes when it returned to idle it was rough, sometimes not.

Popped the hood, noticed the clear fuel filter had some bubbles in it, so I replaced the hoses between the filter and the lift pump, and between the filter and the hard fuel line.
It got slightly better, then slightly worse, with rough running and loss of power in the 1000-2000 RPM range as before, and would sometimes run rough when returning to idle, but sometimes idle smooth if I gave it a little throttle and let it return to idle slowly.

Popped the hood again, watched the fuel in the filter as I revved it. The filter drained almost empty as the engine revved from idle to about 15-1800 RPM, in parallel with the rough running, then filled rapidly with fuel as the turbo spooled, which began to froth in the filter from there up to WOT.

Drove it back to work, then when I started it to drive home, it idled poorly, still ran rough and lost power in that middle RPM range.
About halfway home it started losing power on the highway, and I had to floor it to keep it running. By the time I got it pulled over on a sidestreet, it was idling extremely rough, visibly shaking an inches or two back and forth, and pedal floored only got the engine up to about 1000 RPM.
Removed the plastic fuel filter and connected the hose from the hard line directly to the fuel pump, thinking it might have a leak. Running didn't improve. Opened the fuel cap to add some Diesel Kleen, thinking tank filter might be sludged up, and the engine died almost immediately.

Restarted the engine, running became gradually worse.

I tried running with the hose from the fuel pump feeding from a bottle of fuel, to isolate the hard lines, tank-side hose, strainer etc. Engine ran equally badly, becoming rapidly worse until the engine can no longer maintain idle for more than a second after starting.

I'm trying injectors first, although I wouldn't think those would fail suddenly, and don't think it would run this rough even with a dead cylinder. Next thoughts are lift pump and injection pump timing, although I don't see how injection timing could work itself loose so suddenly. I've ruled out valvetrain or lower engine damage, as those couldn't really be intermittent, and I don't see how they could improve with increased revs.

New primary and secondary fuel filters installed ~4kmi ago.
Valve lash done ~6kmi ago, then re-checked ~4kmi ago.
New engine and trans mounts ~8kmi ago, visual check shows no damage.
New rack damper bolt installed and tweaked ~3kmi ago.

No smoke on start or at any speed.
No milkshake in coolant or oil.

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RIP:
2011 E350 BlueTEC, Schwartz 81k (totaled by uninsured drunk driver)
1964 Unimog 404.1 (wrongfully towed by the city)
1994 E320, Brilliantsilber 208k (transmission shuffled off after sudden catastrophic fluid loss)
1982 300D, Silberblau under a blue repaint 256k (sold for parts)
1995 E320 Polarweiss, 131k (sold for parts)
1995 E300D Polarweiss, 287k (totaled by drunk driver)