I think that only what any of us can say. No one can expect each truck to act the exact same way. I'll just see how my 'experiece' turns out with the autolites.

Yeah, I think that's what I'm gonna try next too.

 

Yeah give those a whirl....

I am about 2 months on the autolite double platinums 5224, gapped at stock gap, and the truck has been smooth, quiet, regular gas mileage. Sometimes I can't even tell the damn thing is running when just crusin along. Just as peppy as it was when I bought it. Just go on sparkplug.com, and check the recommended plugs and gaps, and go from there. They have pretty decent prices on there too.

 

the plug on the left is the correct 'extended nose'

the plug on the right is the 'short nose' version of that same heat range spark plug

notice the used plug on the right of your picture
is similar to the short nose Autolite 39xx series you put in

this may have been a simple mistake by someone who worked on your engine before,
or it might be a legitimate attempt
to reduce pinging/detonation that was happening
in that particular cylinder you found the odd plug in

a shorter nose spark plug design slightly retards the 'real world' ignition timing in the cylinder it is used in. this can reduce pinging for that cylinder only. it is a common trick of the trade in engine tuning. you can do similar tricks with different gaps in different cylinders

the posters above who say this is because of the 4.7 V8
'wasted spark' coil pack system on Chrysler engines are misguided,
and need to study the wasted spark design principles over again
to fully understand how the system works

http://www.gill.co.uk/products/digit...wast_spark.asp

http://motor.com/article_pdf_downloa...article_ID=195

http://www.aa1car.com/library/dis.htm

http://en.wikipedia.org/wiki/Wasted_spark