Code is P0411

Mods, stock motor/intake, stock exhaust with UK Exhaust mod and a resonator delete.

I noticed once I hit 6k, it somewhat throttled itself and there was no "burst" like we are all used to.

Went to Autozone and a few steps they said: Circuit relay defective or fuse, check connector and wiring, or air pump defective or hoses blocked.

noticed it like three days ago and instantly checked the oil level, found i was a few quarts low with no traces of it anywhere. Filled it up and it appeared to engage but no where near what it usually is. Right now I have the factory filter off getting cleaned.

Just broke 70k miles on a 2000 SSM

Does anyone have any resolution to this?