I had a similar problem and discovered the fuel line was sucking air....not so much as to affect normal driving but after some miles, an air bibble would build up and it actually created an air lock in the fuel line when I was going uphill - the bubble moved inside the fuel line (ONLY uphill)....it drove me nuts 'till I found it and felt pretty stupid...I overthought the issue...hope your'e is similarly an easy and cheap fix.