I have an 01 Impala, and when the plugs come time to be changed, I’d likely follow admitted amateur’s course of action - replace the front three, reproductive activity the back three. And $150 isn’t that bad to change the plugs on a transverse V6. My dad’s gotten a quote on his V6 Sonata to replace the plugs - $600!! In order to get at the back three, one must remove the intake plenum, fuel rails, throttle body, coolant hoses, and a few other things. Oh, and the engine must be tilted forward. So, yeah, there’s no way in hell I’d even attempt to do that. I don’t have time.