I have managed get Multiecuscan running on a laptop and connected to the Multipla for the first time today. It has been suffering from power loss, especially up any hill. Acceleration is not great, but it can rev up to about 4-5000rpm when in 1st only, otherwise a max of 3000rpm. Some black smoke when first started and after taking your foot off the accelerator.
The only error code was a low voltage signal from the boost sensor. Guessing this could be indicating a faulty sensor ?
I haven't had managed to check the hoses on the turbo yet but recently cleaned out the EGR valve. The scan shows the valve active. On idle at 100%, with the accelerator down it changes to 1%.
While I have read a number of the posts on here about power loss, any suggestions at this stage would be welcome.

You are describing limp mode very accurately. Do you have an engine light on the dashboard and/or engine fault message? If you clear all fault codes do
Regards
Stephen