I would look into the upgraded HPFP as its basically maxed out stock AFR's are probably being sent through the 200's which is mostly air no fuel the HPFP in the car now probably can't handle higher end tunes.
heres the upgraded pump sadly its the only one on the market right now for N55's so its quite expensive.
http://tuningtechfs.com/ttfs-xdi-35-...grade-for-n55/