Possible misfire causes:
Improper spark plug
Insufficient compression
Incorrect fuel pressure
The injector circuit is open or shorted
Injectors
Intake air leak
The ignition secondary circuit is open or shorted
Lack of fuel
Drive plate or flywheel
Heated oxygen sensor 1 (front)
Incorrect distributor rotor
Have you replace spark plugs, wires, distributor cap & rotor? Do you ever run a fuel system cleaner? I would start with the easy stuff. Hate to take it to a shop and find out it was something stupid like a worn rotor in the distributor. Buy all OEM parts. Use NGK plugs. My guess is though in the end you have an injector screwing up. Let us know.