Chevy silverado 2005 5.3 misfiring

My silverado 2005 just started misfiring.

hi scotty! my silverado 2005 5.3 just started going rough and misfiring and it smells like gasolin in the exhaust, this problem comes and goes and it stops when i restarts the engine. also checked the obd2 and it said p0300. what do you think its the problem?

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