I have a 1.2L Corsa B automatic, and I'm having trouble accelerating. I can only get to 60 mph slowly on flat roads, and about 30-40 on a hill but 70-80 mph downhill. I can feel it hesitating when changing gears, and revs go up but car won't increase in speed.
I've put in a new air filter and am running a cat cleaner through it. Any ideas what it could be and what else I can do? Could it be the spark plugs or the fuel filter?