1984 mustang 5.0 EFi wil occasionally sputter act like it's not getting fuel or firing

First noticed on longer trips, 1 hr, (and after running a can of seafoam through tank) While driving RPMs will drop like it's not getting fuel. Sometimes can last for a mile or two at 60, then straighten out and run fine for another 50 miles. Tried the old clothespin on the fuel lines trick. Seemed to make it less severe happens more often, but doesn't last as long. Also idles at about 1100 rpm, occasionally idle will fluctuate 300-400 rpms while idling the clear up and be fine. Car has been in storage, less than 2000 miles in the last 7 years. Have replaced the fuel filter. I think this is a two filter system. Saw what appears to be electric pump near filter while changing it.  Is this a fuel problem or electrical?  car has 167,000 miles