I would be trying to find a decent garage by you that do diagnostic work, sounds like your friendly ford dealer aint clued up. Couple of suggestions airflow EGR very common had one the other day that wouldnt start because of that was chokeing the engine. Also intresting what ford said turbo fault, im pretty sure you will have a variable vaine turbo on yours, ive none them stick and cause a slight over boost this then knocks the power right back. If i were looking at it would be using fault codes and live data on a road test, shame they didnt give you any fault codes, see if they have got any, if the lights were on it will have stored some