Will a 2000 Chevy truck tail light fit 04 taillight?

No, a 2000 Chevy truck taillight will almost certainly not fit a 2004 Chevy truck taillight. While they might be the same brand and even the same body style (e.g., Silverado), Chevy redesigned the taillights between those model years. The housings, bulb configurations, and wiring harnesses are likely different.