years ago i experimented with spark plugs. but i cant work on my truck now days. in my 2001 dak 3.9 V6 auto trans. all stock save a Mr. Gasket #1487 air cleaner 9" X 2" 30,000 miles ago i had my shop put in champ rc12lc set to .045 gap. at that time i was sure they was to hot of heat range. but they was not bad on heat range. but the center electrode did round badly . my guess is .050-.055. of course this killed throttle response some what. i put in autolite AR3933, at .040 gap. i think it is running better with the 3933. and YES it is racing plug. it is kind of cold. at lest it didnt stop running. time will tell

 

You should just have put NGK's in that beast....

ZFR6F-11....

 

You should also change them every 30,000 miles...
Just my 2 cents

 

you might be right about the plug to use. i have used NGK plugs. they are good plugs. ill just have to keep a good watch on the autolites.

 

a new thing. bob. it started dying if the rpm is 1200-1500 and i let off fast it dies. with trans in gear , in neutral it doesnt die. if i let off slower it doesnt, die. or if i hold the rpm up a little it doesnt die. the spark gap is a lot closer the plug base than the champs. my idea is that with the new spark being farther a way from the piston it is the same as retarding the timing. i think the performance at low RPM after a gear change is better. what think?

 

Not so much in this case Moe...
I think sticking with something in the OEM range is going to be the best way to keep it.
The timing is going to be delt with by the PCM... Not from the plug shrouding. I think if you look at it (pattern wise) you would not even be able to notice the burn difference at all.
As far AS I know the IAC motor gets gummed up on these 3.9's. I would try cleaning it (or replacing it) and the passage and also perform a throttle body cleaning And see how it acts.

Just my 2 cents