A cooler thermostat won't really make it run cooler and even if it did it's not better. Modern engines are designed to run optimally at anywhere from 190-210. Even with a cooler thermostat your fans are not going to come on until their set temp so you're still going to see stock temps.
Stick with oem type plugs. Also even though your truck is supposed to have the updated plugs good luck. The 5.4 is known to be a nightmare.