2.5 V6 feeling a little flat
 

Hi Everyone
My New 03 conny se V6 feels a little down on power compared to my old 01 one. when I first told my Rover expert we did a find a dead Balance valve which I replaced and the VIS system checked out fine. Additionally, he adjusted the throttle cable but neither of these made a real difference so, I just left it there and forgot all about it. The other day though I had to move my old 75 (now a parts car) I couldn't help to notice how much more eager to go it is than the new one. So, I'm wondering what could possibly be causing the new car to feel slower. Other things I know about the car are that the engine was replaced a couple of years ago With a "reconditioned" one and it has a cheap aftermarket exhaust which I'm planning to replace with original Rover one that my old has.
kind Regards,
Thanos