Add 180F thermostat to the mod list.

I don't feel that headers are required for that larger pulley. It's not a 3.4 and that's good. Pull the plugs and look for anything obvious. They may even be fouled and need to be replaced. The 2 degrees of KR does show that you have KR...

What grade of fuel did you say you were using? turbo/supercharged need premium, 93/94 if possible, 91 at the very least. That could do it right there.