Has the forge got the revised piston in it and when was it last serviced? I'm guessing all connections on TIP have been checked , any other boost hoses changed or checked upper and lower? Either that or poss cracked or damaged intercooler.
 
Can't quite make out what your holding but this may help (hopefully)
List of possible causes:
- Intake air leaks
- Faulty front heated oxygen sensor
- Ignition misfiring
- Faulty fuel injectors
- Exhaust gas leaks
- Incorrect fuel pressure
- Lack of fuel
- Faulty Mass Air Flow (MAF) sensor
- Incorrect Positive Crankcase Ventilation (PCV) hose connection

Any one of these been checked or replaced?