I would start by pulling the valve cover off, taking the crankshaft bolt socket and turning the engine over manually while watching the timing chain and valve train to ensure that everything moves the way it should. It is the "cranked up and ran for 20 secs" sentence that makes me think that you should be allright as far as timing chain/cam/valve train goes but I would check this stuff first. Make sure you compare the timing mark at the camshaft and the crankshaft at TDC on the #1 cylinder while looking around in there. I would go from there to the fuel delivery system/fuel quality.

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Jim