98 Cvalier Stalling problem

I have a 98 cavalier 2.4 OD trans, this car has been stalling intermit while driving, but mostly after a cold start and within 10 minutes. Once car is hot it runs fine. Has had a recent engine swap, but all components were changed out and no codes in the ecu ect. Thought it might be fuel pump or fuel pump cut off due to oil sender or something like that. Any help would be swell.....