This is pretty classic description of a clogged fuel filter, so that would be the first thing to do - replace the main filter.

After that, I'd say time to look for another problem, like either your new lift pump is bad or some other fuel problem like an air leak.

Other possibilities include a clogged air filter or clogged tank screen or reversed fuel lines in the engine bay or clogged muffler.

__________________
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