Did you check the timing chain wear (stretch) when you had the valve cover off? A stretched chain will retard pump timing.

Have the injectors been tested / cleaned / adjusted in the past 100k miles or less?

Typically the timing of the injection pump is good for the life of the engine, once it is set correctly, so I suspect you've got some other problem going on, related to fuel delivery.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC