Fuel Pump Problem??

[nacho55]

Little on my Project, it is a 02 5.3 with a 5 speed, and modified harness, and a blazer tank with a AC Delco EP381 Intank Fuel pump, (or I think thats the pump), in my 55 first series truck, its been running a little over three weeks now and I have put about 800 miles or so on it now and it runs great, but the last couple of times I have taken it out, it stumbles and even stalls but will start right back up and idle normal, but then stumble when your driving like its out of gas untill I drive it for two or three miles, then it drives like normal. but if it sits for a couple of hours it will act up again but not as bad like when it sits over night or a few days. I have a serviceable fuel filter that i have cleaned a few times and there was some crud in the filter element but it wasnt completly cloged, could the pump be going bad, or not enough pump, or bad regulator on the fuel rail?
Any thoughts would be great
Thanks