1993 Ford E-Series Van engine idles fine but misses upon ac

Hello, I have a 1993 ford e250 with a 4.9 six cylinder engine. Whilst driving on the motorway it began to missfire upon acceleration. I have replaced the following items since the problem originated , but have not been successful in remedying the problem : fuel filter, spark plugs, wires, ignition cap and rotor, map sensor, have put injection cleaner in the petrol tank,checked the compression (it is sufficient),checked for vacuum leaks. There is acceptable compression and no excessive valvetrain noise, so I do not believe it is a broken valvespring /rocker arm/pushrod/ tappet problem. I believe that it is an insufficient fuel delivery problem. Is it most likely an injector? The engine idles without a miss, but upon accelleration misses horribly. It can be driven , but stumbles and lacks power.Am I correct in my assumption that it is an injector ? Any advice would be greatly appreciated. Thank you.