L322 Since changing fuel pump difficult to start when warm

Fuel pump failed some time ago so replaced it. But since then it is sometimes difficult to start when warm and been standing for some time. First thing in morning starts fine, but when warm turns over longer and then fires but struggles as though no fuel (sometimes even stalling). A blip of throttle helps and drives fine once running. 2004 4.4 V8 - any suggestions appreciated.
Thanks!