2004 saw the reintroduction of the Pontiac GTO (based on the Australian-developed Holden Monaro). The GTO was also initially powered by the 350 HP LS-1 V8 in its first model year. It had an independent front and rear suspension and an upscale full leather interior. Sales did not reach the 18,000 units that GM predicted. The LS1 engine was retired in 2004. Pontiac added the drive-by-wire 400 HP LS2 V8 for the 2005 and 2006 model years at no additional cost. Additional upgrades also consisted of stainless steel dual exhaust outlets, larger Corvette sourced PBR brakes with EBD, larger front vented rotors with vented rear rotors, and functional heat extractor hood scoops. The Bonneville introduced the GXP trim level to replace the SSEi. The Bonneville GXP featured a 4.6 Northstar V8, borrowed from Cadillac, and replaced the Supercharged 3800 Series II. The redesigned Grand Prix made its appearance, and featured a GT and GTP trim level. The GTP's new 3.8 L supercharged V6 now made , up 20 from the previous generation. TAPshift was also introduced as well as a Competition Group package (Comp G).