I've gotten only 27K max out of the copper plugs. Your symptoms were the first indicator for me that they were bad. Even with newer plugs, I've had similar issues occasionally because my truck is sensitive to certain fuels. It stumbles a little when it doesn't like the gas I bought and of course, any inconsistency in the way my truck runs is felt while driving because of the manual transmission. All of you with your fluid coupling don't notice as much.

How long was your truck down? The ethanol could've picked up some moisture which you burned through.

 

If it gives anymore trouble, I have another set of plugs ready to go.

I would have liked to have known what caused this, and my best guess is the new t-stat. I was running a little higher than normal for awhile before it settled into the "normal" area and the stalling stopped. I tried to find a good t-stat, but my local napa went out of business, so I had to settle for a Chinese one.

 

A little higher than normal coolant temp shouldn't have caused any change in the way the engine runs, even momentarily. It could have been a few small air pockets. If a temp. changed quickly because of them, the truck could've tried to overcompensate for that short time.

Either this or I still say the gas could've picked up some moisture.