1988 Ford Ranger fuel

When I first start to drive the truck it has all the power it needs few miles down the road it starts to starve for gas 5 seconds latter its back then gone again it will even do it at idle I have 40psi to the scharder valve when truck is running good when starts to run bad has only has about 30 psi what could be the problem
i have vaccume to regulator and its changes are in range
could one of the fuel pumps going bad or not strong enough to take load