Things such as temperature and air pressure can alter make a big difference on how the engine performs. Id really get it put on rollers to get it logged. If you are in leeds, rtech are only an hour and a bits drive away. If you had a boost leak you would get a fault code of P0299 of underboosting. I had this fault but it was the map rather than hardware.
Think R-tech is about 2 hours away. Stattlers is only 1 hour away so would be my first choice. Im more concerned about the the N75 redaing, it shouldnt be up at 100% for a long period of time.
Now i dont know if its the N75 that cause that or something else can cause it to do that