tire help..

Wow! I never heard that 35's only last 15k miles but have never used them. I have run 40 & 45's. I currently use the Nitto 555 but may favorite has been the Bridgestone Potenza (probably Pole Position for your application).

I also have a 2000 GT and have been told that you will need to remove the quad shock--requiring better LAC's.

Removing the quad shock (the horizontially mounted shock behind the rear wheels) adds additional tire room. With the stock Lower Control Arms, this isn't recommended. LCA=Lower Control Arm. Not sure if this really IS necessary with this size tire, but, if so, shop Steeda, UPR, Maximum Motorsports for some quality LCAs that will allow removal of the quads without worry.
Bridgestone Potenza is a great tire. We have them on my wife's 01 GT - awesome dry AND wet traction. They are not exactly cheap though. Nittos are pretty cheap, but their life is rather short. I think 15K miles is incredibily short!