there arent many roots blowers out there for the v6 besides small companies. With any supercharger your gonna get drastic performance gains. Id reccomend a procharger 11 psi intercooled centrifical supercharger. then you can buy a chip or dyno tune and the necessary fuel upgrades. Those things should run you around 5 grand give or take a few, the procharger alone is 3 grand.
1999 Trans Am WS6
Full Stainless Magnaflow Exhaust, Stainless Longtubes/Off Road Y-Pipe, QTP E-Cutout, HP Tuners, Super Sucker Ram Air Kit, BMR Tunnel Brace/Driveshaft Safety Loop, Hotchkis Panhard Bar, Hypertech 160 Thermostat, CF Whisper Air Lid, Corvette FRCs, K&N, !AIR, !EGR