Rodeo Ra 2.4l Slow  

Hi, i recently bought a 2004 ra holden 2.4L shitbox and fcuk has it been chewing the fuel and driving like shit. You can drive it like a granny alright but after 60kph its weak. You put your foot down and the car makes a big sound and nothing, it just pulls away slowly. Even in first gear it is a little unresponsive. I thought it was the cat converter, so i got that replaced and it ran a tiny bit better but its still shit, symptoms are still the same. Changed the sparkplugs and have done a service , new air filter. Still runs like shit. Any ideas would be much appreciated. My patience is running thin, im close to pooring petrol on it and torching it. Its a tidy little ute but it just doesnt have any go at all. Any ideas?