Had this car since new 5 years ago, 50k miles on the clock. On starting and until full temp is reached the car seems to have "normal " power. But when fully warm it lacks power. Put foot down and the engine responds kicking down but very slow change in speed. Have taken it to a dealer who checked it out and found nothing wrong so am taking it back...would appreciate any ideas. The turbo seems to be working during warm up. Coincidently I took it for its first major oil chnage when the oil filter was replaced. It behaved normally on the way back from the garage but shortly after it started. Have tried premium diesel. Thanks!