help! Td5 poor running / power loss

hello to all you anoraks, put myself in new members enclosure lookin for the men in overalls to help me with a problem with my Td5,a few kind hearted souls told me to move my thread to this site and the head and chin sratches would consult there landy brain boxes and come forward with some solutions so here goes, once upon a time i followed my heart and not my brain and bought a Discovery Td5 manual ES (i know i think it had something to do with the smell of leather).The costs came tumbling in by the bucket load,discs, pads, brake calipers, tyres, clutch, flywheel,electrics,sensors,turbo and of course cheap servicing,but i still love the dam thing, anyway alls ok up to 50mph then it feels as though its running on only 3 or 4 cylinders, power loss and just wont perform. LR dealer has checked it out on test and diagnostic but to no avail, the problem is intermittent any ideas mileage 125k all 12 stamps so well maintained any ideas!!!!!!!!!!!!!!

Anorak ! HUH....

sorry eightinavee if the word "anorak" caused offence just searching for some advice from the ones that know through experience of taking these tonkas apart as the so called professionals at the LR dealership havn't got a clue all advice greatly appreciated

it could possably be the air mass meter
take it to a landy dealer and get um 2 plug it into the comp, saves faffing about for hours, when its over in minutes...spose its the only good thing with them td5's