1997 Ford Explorer Engine Hesitation and Sputtering

Shortly after having work done to fix a cracked exhaust manifold, our 1997 Eddie Bauer started having major engine hesitation and sputtering under normal driving conditions.

While I was deployed my wife took it to a repair shop (after getting no help from the original repair shop) to diagnose and repair. A $500 tune up with new plugs/wires, etc. And still the problem persists. I have cleaned the MAF sensor, cleaned and checked the ignition modules (at Schucks and they did tests which they say are ok). Still the problem persists.

Next is a fuel filter replacement (which is beyond my expertise, a neighbor will help). Is there anything else to look at before the fuel filter replacement? Could bad work done replacing the exhaust manifold gasket, produce these problems? How would I check.

It threw codes a while back (P30, can't remember which) but no engine light, and no more codes recently.