Land Rover Repair: 2007 Discovery 3TDV6 loss of power, landrover dealer, landrover discovery

Question
My 2007 Landrover Discovery has done 40000 miles.I can cruise all day at 70mph approx 2000revs and want to pass lorries taking up 2 lanes of the motorway.I put my foot down to pass i draw alongside and then expirience loss of power.I pull over find a safe place to stop,switch the engine off,wait a few minutes all OK.The AA have been called on 2 occasions and their diagnostic equipment does not show a fault.An independant Landrover dealer cannot find a fault.My landrover main agent thinks it might be a turbo but is no sure.How can i be sure what the problem if no one can get an accurate diagnosis.Is this a common fault with this model and could it be electrical?

Answer
It's probably not something as simple as "changing a turbo."  My guess is there is something going on with the waste gate or the turbo controls.  What you may have to do is find someone who will take the time to go for a ride with a proper diagnostic system connected, and see what the data stream shows when the malfunction occurs.  I think that will be the most efficient path to solution.  The data will probably show something like low boost, and then you will have to manually test all the things that could cause that.  I expect the problem will be a switch, vacuum hose . . . something small and hidden