I switched out the stock plugs during a tune up in June 2018 with AC Delco 41-110 Iridium plugs<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}-->https://mechanicfaq.com/spark-plugs-for-5-3-silverado/ per the AC Delco book and Rock Auto lookup. Since the tune up, I've always felt the gas mileage has come down. I'm getting 14-15 MPG on the highway keeping it under 70 MPH, when I used to get around 17 MPG. I chalked it up to ethanol fuels.

I just read that AC Delco is no longer recommending this plug for 2000 - 2005 5.3L vortex engines. They are now recommending 41-962 Platinum plugs.

Does anyone have details on why they made the switch? I'm curious to know if the 41-962's are more efficient for this engine and if I should make the switch to the latest recommendation. The $50 cost will quickly be returned if I get 3 MPG back.

Is anyone else running the Delco 41-110 plugs in a 2000 to 2005 5.3L and noticing a drop in fuel mileage?

Thanks.

 

From what I found they are cheaper alternative. See the attached PDF

I believe the original plugs where 41-985 Platinum with a .060 Gap. This was discontinued and replaced by the 41-110

41-110 is Iridium With Recommended .040 Gap
41-962 is Double Platinum With Recommended .040 Gap

 

I read a lot of posts about folks complaining about reduced mileage when using those 41-110s. This was even with folks that originally used the 41-985s pre-gapped to .040" too.

I lucked out and bought a brand new box of 41-985s so I have no experience with the newer ones!