1980 300SD. Virtually everthing done now. filters, dampener screw, valves, return lines etc.

Still stalls only sometimes. Yesterday I could floor the pedal with no increase in rev's or acceleration. Two minutes later was fine. I am thinking injection pump or clog somewhere. No shop seems to be able to find a clue. What could be going on?

Algae in fuel? (I am in Las Vegas though). Clog in tank?