My 15 Sonata Eco just hit 128k miles with no service issue history. I regularly change oil and perform maintainece. Last night out of nowhere when I accelerated from a stop the car had very little power. In first gear it would run out of steam and with the peddle floored the top RPM was very low. In park I floored the throttle and at 4k RPM it just bucked. I'm thinking fuel pump? No check engine light. Now this morning it's fine after letting it sit. Any ideas? I was wondering if the fuel pump would do it but I have no clue as to what kind of fuel system problems are possible.