LS6 intake, Ported throttle body or bigger one
Longtube headers and off road y pipe
Converter. For an A4, it makes a big difference
Rear end is fine for now. Don't worry about it. Just keep in mind they are weak.
EGR and AIR delete. Cruise and traction control delete. Ac if you don't need it.
I have a 2000 T/A, I've done lid, headers, cat back, ls6 manifold, ported throttle body, and dyno tune and it's a super fun daily driver, I tried to keep it as practical as I could while still having some comfortable power. If it's your daily driver or a nice weekend car don't delete your AC or any of that stuff and definitely keep your cruise control (what does deleting that do?), to me that's just ruining the car and depleting the value unless it's a drag car only. I've deleted my AIR and EGR only because I have headers and that's probably all I'll be deleting. Different strokes for different folks I guess.
__________________ 1999 Fully Loaded Torch Red FRC
JBA longtubes w/ ORX-pipe & Corsa Pace Car Axle Back.
Vortex Rammer w/ FAST 78, 25% PB UD Pulley
2004 ls6 PCV/Valley Cover w/ Mike Norris catch can.
160 Degree Thermostat, Katech belt tensioner Monster Stage 2 clutch w/ 18lbs flywheel, Tick Master, & MGW short throw.
353rwhp/363rwtq Tuned by Boost Performance *SOLD*2000 Trans Am WS6*SOLD*