New spark plugs and oil but engine still a little rough? Not as smooth as you remember?
Engine start to misfire when when you try to run higher boost? But on normal or lower boost it is perfectly normal?
Most probably your old ignition coils need some refreshments and this will be a good start.
I changed the ignition coils without changing the 15k km plugs, the engine runs smoother and no more misfire at 15psi of boost.
The product part number on top of the coils cross checked with the eldor manufacturer number. No any brand stamped on it. Just the manufacturer part number.
This will be one of the greatest refreshments you can have and ckme with a competitive price.