Pontiac Grand Am

Hello I have a 99 Pontiac Grand Am with a 3.4 liter engine . I have recently acquired the car lately I've been noticing that whenever the car gets hot the engine Lopes and then and then dies. But only at low rpm? I took it to a mechanic and had him put a pressure gauge on the fuel rail he said the fuel pressure is low about 40 pounds. I don't know whether I need a new fuel pump it only does it in hot weather .
can anybody help me !!
:banghead:
Thanks.!