I know on the 97-03's they are behind the windshield cowl at the bottom of the windshield. I'm not sure but they may be accessed the same way as the 97-03's.
On the 97-03's you need to remove the windshield wipers and remove the black plastic fasteners on the cowl then lift the cowl up to remove. On the pass side you should see the intake air box for the A/C. The filter resides in there.
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Bobby
Died 5/1/08, resurrected 5/15/08
ASCD SD hood, 17" Bullitts, Overkill PCM, 3.4" Pulley, NGK TR55IX, K&N 9" cone filter, JimmyC D/P, U-bend removed, Flowmaster 40 series, Hooker big bore tips with resonators, S/B brake lines, drilled/slot rotors, GMPP handling kit, KYB struts, F&R strut supports, HID's, LED's, 2.5" Air Dam, red GTP overlays on custom badges, white rear insert.