Welcome Zimona,
Check out 97GTSTANG's threads on advice for first mods on 4.6s. Actually, I should start a FAQ for new forum users...
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98 GT
Bassani X-pipe, Dyno-Max Cat backs, 3.73 gears, Steeda shifter, FMS pullies, 87mm MAF, Roush cold air kit, Eibach springs, and Zex 75 shot