I might have over looked it..but I didnt see a larger Downpipe in your sig....our Hot-Air cars really love larger downpipes (and while you are at it port out the exhaust elbow)
While you are over on that side taking stuff off...check to see if you have cracked headers...if you do....our cars really like headers as well as a downpipe...I dropped about .8 and added 4mph just from putting Headers, and a 3" downpipe on my car!