So I have only had this car for just over 3 weeks now, semi-automatic Corsa 2013, first few weeks it drove well, I used the manual option and gear changing was a beauty, I went to fill up my tank the other day and I think I filled it too much, I never like to go beyond half a tank, but the car felt sluggish afterwards, turned on my AC to try and burn some petrol, and that took forever, after two days had a trip to the country side with a lot of hilly roads as automatic goes it struggled, I thought it was just normal for automatic cars, but now on flat roads, I need to press the gas harder inorder to get from gear 1-3 and then the manual mode doesn't seem to want to respond to gear changes, now stuck driving the auto mode which is even slower. I checked oil levels it's half way, so will buy more on Monday, but before I take it to the garage can someone give me a rough idea what might be wrong? The car is only 1 year old and with 6000 milies on the clock so certainly it can't be the engine? Or gear box? It also has a ratting sound coming from the engine which wasn't there before? Could it have something to do with fuel pressure? The car was also serviced twice, once before the car was sold to the dealership and again before the car was delivered to me. Certainly any major fault could have been picked on? Am hopeless with cars.