Well figured that out. Wasn't fuel related at all - the blow off valve was leaking on the lower part of the gasket and it would slowly discharge when you let off the gas, then let it all out at once through the turbine hence the undulating noise. The blow off valve was not working, and essentially when it hit 5 you'd hear air escaping then the car slowed down. It will now hold 4 psi, and still opens at 5, but the car doesn't act like it hit a net anymore. I am curious if adding a BRPV to the setup will be a viable option to go for now.