[CP911]

I think any lag or hesitation is with the 8-speed auto slushbox, not the throttle. When I did my Performance Center delivery, they gave me a RWD 8-speed even though I purchased the 6MT. The auto had hesitation at times when accelerating from rolling stops or slow speeds. My 6MT, however, does not have this issue. The motor revs when you hit the gas. Only time it won't take off immediately is when I'm simply too low in the rpm range (<2k rpm) for a given gear. Engine still revs, but there is obviously no torque available at such low rpms.

[KrispyM240]

I used to tune cars for a living, predominately Mustangs. Quite literally everyone complained about throttle lag and there was actually a table for throttle input vs. throttle response. Super simple really, this much input equals this much %.
While this is very basic and will help for the most part, you will also want to match the torque curves and some transmission settings to help clear it completely to emulate the good ol' drive by cable "feel".
With that being said, Pedal Commander etc. are solid choices but they're essentially one trick ponies. A solid tune will do wonders. Personally I am not familiar with the changes that JB4, Dinan, etc. make but if they don't beef up throttle response they're just not worth the money.
Now if someone could point me in the direction of any sort of tuner/piggy back system/handheld flash tuner which would allow me to make my own changes, that would be phenomenal