!!!!HELP!!!! haunting missfire wont leave!!!!

the timing chain has maybe 30 miles on it fuel contaminations is a possibilty but the thing that baffels me is that its done the same things with two different motors thats why we figures is has to be the car weve gone thre different distributors control boxes cabs wires plugs went threw the wiring back to the harness that goes to the main harness and cleaned up all the bad spots i mean i dont know what else it could be...:-(