Help With P0300 Random Multiple Misfire, replacement motor Options

[nb_corolla]

Hi Everyone, new to this forum so please bear with me. I have recently replaced the motor in a 2001 Corolla CE in hopes of making it road ready for my daughter. The previous owner had an oil pump failure which let to the car's demise. After carefully making the engine swap, the car fired right up and runs quite well, EXCEPT...at high rpm it misfires...and throws a P0300 random multiple misfire code. It has new plugs, and I've replaced the intake manifold gasket suspecting it's a vacuum leak (the car idles a bit too fast)...no luck. I've also changed the camshaft sensor (from the previous engine) and am about to change the knock as well as the crank sensors. Can anyone offer any other suggestions as to what to look for in terms of high rpm misfires? thanks

[DrunkenDwarf85]

maybe a restricted fuel filter could be causing it, try replacing that