As CPTAFW163 has stated as part of his post, the OP needs to check the plenum as usual. Once that issue is taken care of, I too would stick with the Champ OEM plug on a stock motor.

 

i have the depleted uranium p-136 modular plugs!! AWESOME POWER!!!

 

Autolites or the Champions are the best decision either which really there both great choices I've tried both and they ran awesome, Also I can tell you this right now. Stay Away From Anything Bosch. These trucks do not like them what so ever.