Several possibilities: fuel filter may be plugged, fuel pump may be going bad and under-pumping. Ignition system may have a problem, or charging system may not be putting out enough voltage to power the ignition system (but usually accompanied by no start /low battery condition) If dash warning light comes on when this happens, have a code check done (most large parts houses do this free) Also have charging system tested. From what you said though I'm leaning towards the filter or pump as the cause of your problem.