FWIW, this is from Perplexity...
https://www.sixityauto.com/8-pcs-ng...hevrolet-k1500-5-7l-5-7l-5-0l-2024103095.html
https://www.chevytalk.org/fusionbb/showtopic.php?tid/206503/
For a 1999 GM 5.7L engine, the recommended spark plug gap is 0.060 inches (60 thousandths of an inch).
This gap specification applies to the factory AC Delco platinum spark plugs that were originally used in these engines.
However, it's important to note that GM has since revised their spark plug gap recommendations for these older models. The current recommendation for newer replacement plugs, particularly iridium spark plugs, is a smaller gap of 0.040 inches (40 thousandths of an inch).
When installing new spark plugs in your 1999 GM 5.7L engine:
- If using AC Delco platinum plugs, maintain the 0.060-inch gap.
- If using newer iridium plugs, use the 0.040-inch gap.
Always check the gap on new spark plugs before installation, even if they come pre-gapped, to ensure proper fitment and engine performance.
joe