That 104 booster is garbage. As is most octane booster. Your not at 104 anything. I'd be surprised if you added 1 point to your system. ( 93 pump with booster would be 94 octane ). If you have access to race gas, add a few ( 3 gallons) , then fill up with pump ( 91-93 ) more than likely it will go away.
Also how hot was it ( ambient temp ) when you run an open cone the intake temps tend to shoot up real quick. Which would lead to kr as well.
Even on a 99 I would suggest headers before any pulley drop. And even after headers I'd only drop to a 3.5 max.
