Gears being done, what next?
 

Ok, I've added a K&N air filter and ordered 3.73's and the Speed-cal (will be installed next week) on my '02GT convertible (5-speed). What should be the next mod? Under-pullies, exhaust, MAF......? My thoughts (based on responses here and other') are as follows:

Under-pulley - Steeda
Exhaust - MAC long-tube headers, MAC H-pipe w/cats and 2 chamber Flowmasters (my concern is will I get the bang for the buck or will I need some additional enhancements like improving the Intake and/or Heads, pistons, cams....). Is there an Intake available for the '02GT?
MAF - I have no idea
Others - ?

My long term goal (maybe not so long term :p ) is to compete with the Camaro's, Firebirds & TA's of the world SS & Z28 class) and maybe give my buddy (who drives a 2000 Corvette convertible) a scare or two. I haven't won the lottery (yet!) so money is a concern, thus no Blower for the intermediate future; maybe a year or two from now it could happen.

Recommendations please?

Next should be a new shifter and some under-drive pulleys...

If you are using the car as a near-daily driver, I wouldn't go with long tubes due to clearance problems (especially if you plan on putting in some Eibach springs or something...)
Maybe some Ford Motorsport shorties would be a better idea....

Get yourself an X\H-pipe (offroad system if you're in a non-emissions testing area)....

The stock cat-back system is not very restrictive on the 02 GTs....
so a cat-back will basically change the sound.... not much else....

Hammer is right about longtubes. My car is lowered over 2" and I only have slightly over 3" of ground clearance under my cats because of the longtubes. I am very careful and try to take everything at the right angle. so I rarely scrape on driveways or speed bumps, but there have been a couple times when the cats scraped just driving along due to humps in the road that I couldn't avoid without hitting something else. If you are willing to put up with the ground clearance issue, they definitely add noticeable power - I have pulled away from a couple of stock 5 speed 99+ GT's without a problem since getting them.
If you decide against longtubes, I would just get an H- or X-pipe for now and skip the headers because shorties don't seem to gain much power at all on the newer cars (I've heard maybe 2-5 hp depending on what other mods the car has). In my opinion they are not worth the cost and difficulty of putting them in unless they are one of the last mods you are doing to try to get every last hp out of it.

In response to the long tube headers limiting ground clearence...does any one know who makes them with the most clearence.....or is the X/H pipe that causes the problems........my buddy had a '95GT w/ shorties and Xpipe...his cats scraped all the time<------they were punched so he didnt care.

Send back the 3.73's and get 4.10's...trust me!;)

I'm pretty sure that headers on the 4.6L Mustangs are not worth the money at all. I would definitely go with exhaust next, including cat-back even though the stock cat-back exhaust on the '99-'02s flows pretty well. Not only will you notice a little more horsepower, but the sound is something that you will greatly enjoy. I have an off-road H-pipe and flowmaster cat-back exhaust and love it!
As for the 3.73 vs. 4.10 gears, I would stick with 3.73 if it is your daily driver. That is what I have and it's pretty aggressive. The improvement in torque will be amazing whether you get 3.73 or 4.10, and 4.10 probably wouldn't be too much fun for every-day driving.
I'd say after the exhaust your best bet is a short-throw shifter (steeda tri-ax is good) and maybe some suspension. The stock shifters are just horrible. Good luck.

Considering you have a 98 GT 3.73's are a sufficient gear. 99+ GT's are much better suited for 4.10's because of their better heads, higher compression etc..I have 4.10's in my 02 GT(5 speed) and its a daily driver. 3.73's in a 99+ GT will put you BELOW the traps of your powerband.