I ran Bosch Platinum plugs(the regular plugs not the Bosch 4 plugs) in my 1990 C1500 Chevy Silverado with a 5.7 350. I also put a cap androtor and a new set of Factory plugs on it. It did seem to have a miss at idle also, but never hit a lick. We just figured it was due to the Edelbrock intake, JBA headers, ASP underdrive pulleys, Hypertech Themomaster chip, 160 Degree thermostat, K & N filterand an exhaust sytem from a muffler shop with a glass pack that made it seem like a miss. And I later designed and built a ram air setup for itthat made a hell of a difference. The ram air used the stock air box. All I did was notch the air box spacer unde the box and turn the air cleaner with the air tube facing the drivers headlight and the tube from an 1985 chevy truck was used to attach the air box to the air catch tube that was attached to the radiator core support with a holecut in it. The air was drawn through the hole and directed upwardby the way of the metal tube angled upward. I never had any problems with rain or anything.The plugs did increase the MPG.
2004 GMC Sierra Extended Cab- Sold
2014 GMC Sierra- Stock