Have you swapped the plug between cylinders?
Anyone done a compression or leakdown test?
Generally you are describing a problem with the cap, either a scratch, crack or dirty spot. But you had said the cap had been swapped out.

I do know one thing, make the problems go away before you Squirt it otherwise you may still be chasing the problem and trying to tune at the same time.

Cheers, Charlie
If It ain't broke, Modify it!
87 Montero turbo Converted back in Spring1989
95 Montero SR 3.8 DOHC Only one?
93 Pajero 3 door 6G75 Mivec with paddle shifted 5 speed
Then a Gen2 SR with full coil independent suspension.