1997 Holden Commodore engine misfiring under load

Engine Performance problem
1997 Holden Commodore 6 cyl Two Wheel Drive Automatic 200.00 miles

hey I have just recently serviced my commodore and put injecter flush in tank . After washing the engine down I noticed on the test drive it was misffiring and backfiring mainly underload. I replaced the spark plugs and leads checked fuel injectors ok. Ckecked blocked catalyc converter ok, found runing pretty much th same wen disconected the no and no sparkplug leads im thinking it may be crank angle scencor or coils wat do u think and how would I go about confirming problem with coil
cheers