just got back from first trip, towing caravan with my new purchase ,i.e. 2.2 omega cdxdti. All was well until, overtaking a HGV , i changed down to fourth gear. Suddenly i lost all power and the emmisions light came on. I managed to pull over and turned off the ignition.I restarted the car and all was fine again until the next incline. When i changed down to fourth the same thing happened. It seemed, when under pressure the engine would die. the problem recurred five times from wigan to taunton.Without the caravan the car worked fine.The caravan is only 85% of the kerbweight of the car.The problem recurred three times on the return journey,once it faded in fifth gear.Has anyone any ideas why this is happening.