I have a 99 GT 5 speed. I have been trying to figure out what mods I would like to start out with, that doesn't require tearing the heads off of the engine. I want a comfortable interstate cruiser, that will run 13s in the quarter. Here's the plan: 3.73 gears out back, h pipe without cats, flowmaster exhaust(American thunder or force 2, whichever is quieter), and C&L plenum with 70 mm throttle body. I have already installed a cold air kit as my first mod. Can anybody tell me what to expect out of this combo as far as drivablity and performance issues go? Does anybody have a similar setup that they can give advice on? I also recently purchased a CD that has all of Ford's shop manuals that pertain to my car on it. It rules, and I only paid 10 bucks for it! Any input is welcome, thanks all.