hi bro

had similar problems myself, the following info is what Ive gleaned from very good guys here

plug gap mate ? 0.65mm ? brand of plugs ?

You've had the head off ? check the earths and grounds especially the one which runs from the rear of the plenum chamber to the block, check its 100% good earth and no broken damaged wires

the later (I THINK) was my problem, the misfire was just about 4000rpm