I don't think it a colder plug or cooler stat is going to solve your problem.

Have you double checked your firing order? It sounds to me like a misfire. I would for sure do the cap, rotor, plugs (who cares what they look like) and wires. I would say your beating a dead horse till ya do them.

 

I dont know if it was mentioned or not but did you check your plenum gasket for leaking? pooling oil on the bottom of the intake manifold. it's a common problem with the magnum motors. with that many miles on your motor you may want to check your pvc valve to make sure it's free, it could be stuck shut. (may not contribute to the pinging though).

if it's ok, then i'd suggest getting a can or 2 of sea foam and doing a combustion chamber cleaning... suck the sea foam in as directed on the can and let it sit for a while (10~15 minutes) then fire it up. white smoke will come out so dont be alarmed by it. then you can also get some BK44 fuel injector cleaner and mix it in a tank of premium at a high concentration, 1 can to about 8~10 gallons, then go drive it some. this will get rid of the gunk built up on the injector tips. if after all this you still have a problem, yank the o2 sensors and spray the tips liberally with CRC's electronic component cleaner (leaves no residue), let it dry and re-install them.

 

i have durango 5.9 and mine makesa noise like if you where shaking a spray paint can but it only does it at high rpms