Hi Slick,
As I was reading your first post I was immediately thinking it could be a wiring issue. Unfortunately there's a lot of "dartboard-diagnosis" that goes in the motor industry these days. After 15 years in the industry for more than one prestige brand and providing technical support to a network of 65 dealers across Australia, I had simply had enough of people not wanting to do their jobs properly and simply just replace parts until they had fixed it.
The turbo's in these are VGT (VNT/VVT, depends who you ask). They have the ability to vary where the exhaust gases hit the turbine by using an actuator which changes the position of the vanes. This actuator is run off a Pulse Width Modulated signal from the ECU and with a standard multimeter it can be difficult to monitor the signals, especially when the vehicle is stationary. The best thing to use to detect these signals is an oscilloscope and someone to watch it whilst you drive it.
If the turbo actuator isn't getting the correct signals, it will not move the vanes into the correct position and therefore you won't reach the desired driving characteristics, ergo your vehicle goes into a limp home mode.
Knowing that the ECU and the turbo has been replaced (I assume a new actuator comes with a new turbo?) the wiring is likely at fault (providing that your fault codes relate to turbo faults). Wiring can be easily checked with a multimeter by unplugging both ends of loom, from the ECU and the component, and checking the resistance along the wire. A healthy wire usually has between 0.3-0.6 Ohms. Any higher and there is more resistance and any lower and it could be short or open circuit.
Your best bet would be to trace along the wiring loom from either the ECU outwards or from the turbo back to the ECU and check for damages.
Not in the same location, but also a concern to many diesel Jeepers, is the boost pipe that comes out of the intercooler and into the inlet manifold. You haven't mentioned any noises, but they don't always make loud enough sounds to easily distinguish the pipe being split. I would recommend checking it for splits and tears whilst you're in the engine bay.
Hope that helps some way?
All the best in your diagnosis
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