I just installed the Strup header ... getting a little hiss when I'm on the throttle under load. Anybody else have this? Is this normal?

you probably have an exhaust leak. go and re-tighten everything up

u add that graphite donut from the oem header?

Sounds like an exhaust leak. Check your donut gasket.

Did tightening everything correct your problem?

hmmm he never posted again. so i assume success that donut is key