what am i doing wrong with my GT . why won't it go!!

Hey everyone I need some help from the guru's out there. Here is the situation. I have this 2005 Mustang Gt. I put a C&l cold air intake and A Diablosport tune. After perfecting my times at the track i got the car to run 13.59 in the 1/4 with a reaction time of .052 top speed of 102.65 now in the last week i went and put on the Steeda underdrive pullies, Put a set of Magnaflow exhaust and Reflashed the car with the Diablosport 93 C&L tune and ran 93 octane in the car my best time has been 13.572 with a reaction time of .047 at a top speed of 104.50 . Now i have been at it and cannot believe that with the pullies,tune and the exhaust the car did not get better. what did i do wrong? any suggestions. or maybe i have something else that i need to do. I am going to put the Zex nitrous kit on but for now i need to get the car right. can anyone help . Thanks in advance. :doh: