That's a good suggestion about whether or not you have a FCD. But I find it hard to believe that with all the mods you have that you don't have one. I would also check to make sure you didn't accidentially set your B/C back to AC (internal wastegate set up) and make sure you have it set for an external wastegate set up. I would also check your timing. If its off, that could cause some serious sputtering at higher rpm's under hard boost. One more thing could be dentonation. Make sure your getting enough fuel in those cylinders at higher rpm's. Do you have an EGT to be able to keep an eye on those exhaust gas temps? Who did the custom fab work for making the TD06 with an external wastegate? As you can see there are a couple of things to try and work out. If you want we can meet and maybe get a better idea of what may be wrong. I not claiming to be an expert on the 3s-gte engines, but I have worked on them and sometimes sharing different ideas are beneficial.