W210 1998 MB E300TD 281k miles

Couple weeks ago I was enjoying the 600+ miles per tank....though on the next fill up, i got less than 400 miles before the gauge was pointing at 0. I thought there was something wrong with the fuel level sensor, but then when I filled it up, it took 19 gallons, as usual.

I thought because I added a stage 1 tune to it---since before the tune, I had 600 miles. Immediately after tune, 400 miles. So I thought that was the cause.... So I removed it and returned it to stock/factory tune (with EGR disabled).

Same problem.

Oil change, all fuel lines at the IP replaced, all filters (yes, including the tank strainer) replaced.

Thought it was a faulty waste gate transducer, so I swapped it with the EGR transducer. Same problem.

I serviced the transmission and differential fluids about 2000-3000 miles ago

Maybe bad batch of diesel? I tried out a bunch of gas stations, including ones that 18 wheelers use. Same problem.

Tires are brand new Michelin with proper pressure.

So what do you guys think? Fuel injectors? The PO says he never had them serviced, and I'm led to believe him. It looks original.