i bought a 325i m20b25 its been hit no worries about that the car runs great except n all theres just one problem that bugs me. the problem is when i push it up to 4k rpm and keep it steady then it will drop from 3k rpm back to 4k rpm then it will shift. im thinkin it might be from my spark plugs or wires or something or my tranny... someone guide me through please.