The turbo is controlled by the PCM using the MAP, MAF, EBP and the EGR valve.
The solenoid is the actuator. Check the MAP sensor hose, not only the nipple on the intake, but the entire hose. Follow it up to the sensor. That sensor is on the back of the triangular bracket on top of the HVAC box.
The MAF sensor is in the air intake tube, just prior to the turbo. The only plug in sensor on top of the tubes. Don't use anything on this sensor except MAF sensor cleaner. Anything else could contaminate it or render it non-functional.
The EBP sensor, I already wrote about.
EGR valve, I have a serious hard time believing that a dirty EGR valve could cause turbo issues, but whatever. Might as well pull this and clean it up too.
Procedure for cleaning this is use carb cleaner only, keep the liquid and the junk out of the little holes. Full write-up is
HERE.
If these sensor cleanings and the replacement of the VGT solenoid do not fix the problem, you may have to get this to a Ford Dealership that KNOWS the 6.0 They can be a challenge to find.