91 240SX IDLES FINE BUT CUTS OUT BETWEEN 55 TO 70 MPH HELP!

[240SXREX]

Ok got a diagnostic done on the 1992 240sx hatchback, it came back with no codes. I changed the fuel filter, I checked the maintance records, it has a new fuel pump 3yrs ago, I replaced the valve cover gasket(thinking the oil was burning out the sparkplug) replaced the sparkplugs. Now when you get on the interstate it's fine for about 5 or 10 minutes after that if you are going 55 it will cut off and on(doing a jerking surge affect). When you get past 70 mph it stops WTF:confused. I'd like to hear somebody figure this one out .

[240SXREX]

It was also sitting up for a year and a half with a 1/4 to 3/8 of a tank of gas. Maybe water in the tank, I'll get some stuff called heat to get it out, maybe that will work cuz water will stay even if you put a full tank of gas or fuel injection cleaner.

[240SXREX]

Problem fixed, it was the fuel pump filter clogging the pump.