Its definately your custom Magnaflow exhaust. You'd be amazed as to how much torque you lost by doing a custom job. I was very shocked when I had my custom 2.5" exhaust done, and I thought I had more torque. Its crazy what the mind can make you think just by changing things around.
Your best bet is to get the GTR system or go back to stock. Im sure GT-R can chime in and help a little.
Your best bet is to get the GTR system or go back to stock. Im sure GT-R can chime in and help a little.