In my 2003, it was the EGR, both times. No CEL.
If a re-start "fixes" the turbo for a short period of time, that's a clue. The EGR on the 02-03 wears out and needs replacement every 100-200k depending on driving conditions. There is no rebuild.
I also replaced and inspected everything you list before finally arriving at the EGR. By the time my replacement failed, I forgot, and did the same steps again!
*from what we can determine, the shaft in the EGR that opens and closes the valve deforms and wears against the bushings, losing the seal, which in turn causes discrepancies between the MAF and boost pressure readings, making the ECU think that there is a failure in the system and it turns off the turbo as a default safety measure. The EGR will start dripping oil as the seal starts to fail and allows more of the oil-vapor filled boost air through to the cam chamber of the EGR, but that in itself is not "failure", and my EGR went for 50k+ miles with oil dripping before going into the turbo shut-off mode. An EGR block-off plate will reveal very little, because the pressure is escaping out the cam shaft seal, and not the exhaust side.