I am tuning a 2013 Focus ST and I am running into the same issue with no limit active, to combustion stability limit, to insufficient fuel flow during my pull. Boost comes on strong then power it pulled by the throttle body, then drops drastically around 4500rpm. I have searched for all torque limiters but I am not seeing this torque rate limit you speak of. Would you mind posting a picture of it or sharing it's location and what you changed it to? This had given quite the headache.

Thanks,

Kris