Engine Misfire

Hi Everyone! We just purchased a 1998 Sport and right off the bat we have had issues with it. The engine light came on and gave a P0303 code. Easy enough...we had the plugs and wires replaced. The truck ran great for about 2 weeks and then the engine light came back on with little power in the engine, runs very rough and is giving a P0300. We took it back and had the coils, timing belt, water pump, pulleys, tensioners and all 3 serpentine belts and the Crank sensor replaced. It is still running rough and same P0300 code. Any help or direction from here would be appreciated very much!!
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