Even though the fuel filter is new, remove it and blow through it. Is there any restriction? Perform fuel pump draw (+20" Hg vacuum), pressure (5-7 PSI) and volume (~1 qt in 20 secs of cranking) tests using an external fuel source rather than the vehicle's fuel tank. If you don't want to do it yourself then find someone to do it for you. This is a fundamental check for diagnosing a fuel delivery problem.
This will help determine whether the problem is isolated to the fuel pump's function, including whether there is insufficient stroke on the fuel pump pushrod. If the cam's fuel pump eccentric or the pump pushrod are badly worn or the rod is sticking in the out position, there won't be sufficient stroke to operate the pump efficiently, even if the rest of the fuel system is in perfect order.