06 Mustang GT with Roush charger. New injectors and fuel filter. Fuel pump a couple years old.
The engine stumbles badly durring WOT and on a roll. Does not seem to stumble at WOT from a full stop, has boost.
There are no codes.
Brief history. The car has been in-town driven for the last few years. I hadnt even noticed this issue until i took a highway trip, when going over a mountain, i noticed that if i push the throttle deep and go into boost, the motor stumbles badly. Otherwise, if light throttle application is used, there is no issue and its good all day.

Does this sound like a wastegate issue? Where should i look first?