Boosting issues

It sounds like your Power-train control module is limiting the boost as soon as it senses that it is too high. The best thing to do to verify that there is no concern with the add ons you have done is to take it back to stock form then see if the problem persists. That is what they are going to tell you if you take it to a Ford dealer, I know because I set the policy at my dealership. The best thing to start with is to retrieve the codes from the PCM then go from there. One thing that is a common failure is the boost solenoid that is mounted between the firewall and the engine (on the engine bracket), but you will normally have a code associated with that.