Originally Posted by StarzTA17
Also there was a thread on here where a sponsor was building a turbo kit and said they used the stock manifolds instead of shorties b/c the stock manifolds flow so well. So I wouldn't expect a ton out of shorty headers although LT's are generally worth it. Although to get the best results you would probable want a tune as well.
The shorties will give you a deeper sound if that is what you are looking for. The stock headers do flow well but if you want the deeper sound go with the shorties.
As for long tubes depending on the state you may not be able to get them. (ie. California) Usually LTs will increase high end torque while shorties will increase low end torque. With LTs you also might have clearance problems and you would also have to change out your midpipe for sure. The shorties fit with stock mid pipe and you won't have to change it out and can do so later down the road.
With the mid pipes though you will have to decide if you want offroad "no cats" or catted (probably with high flow cats compared to stock) and between x pipe or h pipe. Most go with the x pipe but you will have a more noticeable rasp if you do decide to go with the x pipe.
With gears as others have stated you will have a noticable decrease in mpg. But you will have better performance. The performance package has 3.31 gears which isn't too bad of a hit on mpg. You may want to go 3.73 however.
With a cold air intake you may see changes in mpg +/- depending but you will get more sound from your engine. The stock air box is pretty effective as is and you may want to spend that extra money on a tune, gears,exhaust parts, or one piece aluminum driveshaft. With the driveshaft you will be able to remove the speed limiter so you can reach a higher top speed than a soccer mom's minivan but this will require a tune. Gears also require a tune and very likely a professional install is best. The driveshaft may be something you want to consider down the road as it will be rated for higher speeds and also reduce rotational mass. I haven't seen anyone relating the driveshaft change to mpg increases but I'm assuming it will only help.