Hi, I have an 05 sti with a blown head gasket. I sealed it up and it hasn't given me any problems but I've been misfiring past 5-6k rpms (this happened before my head gasket blew). I have switched out spark plugs and inspected coil packs. I've also cleared all my vacuum leaks. I have an exhaust leak as well in my resonator. The car sometimes has trouble climbing up at around 2-3k when it's cold but is very subtle when warm (loss of power, rpms minor jumping etc). I am most likely going to replace the motor but until I have it fully built I'm dailying this motor. Any ideas on what this could be? I don't have a reliable mechanic in SoCal to help me diagnose this stuff . I am very new to owning a subaru so I don't know what common problems to look out for.