About 3yr. ago I changed the factory plugs on my stock 2000 5.3L w/ NGK Iridium IX plugs. At the time these plugs came w/ an 0.060" gap and my Haynes manual (bought ~5yr. ago) also has an 0.060" gap listed for the 2000 5.3L.

I was just looking today at what plug is now recommended and was surprised to see every replacement plug now has a 0.040" gap on NGKs website.

Anyone know why the recommended gap changed from 0.060" to 0.040"?

Should I now go back and gap my TR55IX plugs from 0.060" down to 0.040"?....they only have ~22Kmi on them.

Thx.