I just changed mine to AutoLite XP Iridium plugs (01 LS V8).
enerpulse pluse plugs $25 average each, and they do work, seen as much s 10 whp on the dyno from these plugs, I switched to them over a year ago and get more than 30mpg highway as well, am currently r & ding iridium versions of the plugs for enerpulse currently and they are worth every penny, every customer I've sold them to have been more than satisified.
platnium 4's suck... i have seen cars fail smog because of those plugs