well thanks for all the replies and suggestions..actually I had the CAT changed last year when I had the same problem,I put in an Aftermarket CAT. It looks a little bit smaller than the original..I also had an Supersprint exhaust installed while I was doing the CAT..the problem was solved when I put in the new CAT but now it seems to be coming back..I also had front and rear o2 sensors installed..not sure if the sensors are failing..but no check engine light..

The plugs were changed about 20000 miles ago..the problem is that once on the highway I am ok..i can get decent power its when I have to stop and start moving again that the car feels like a non-turbo four cylinder and can't seem to get moving ..i can feel as if the exhaust had hole or somewhere there is an leak..but can't seem to figure it out..

will a compression test on the car tell me something..

thanks again