spark plugs

I thought I'd get busy and change the plugs on my '04 XL Denali -- 6.0L, 75000 miles. I bought it recently and doubt they have ever been changed. I was set to pay through the nose for the recommended Iridiums, but AZ had Autolite 2X platinums on sale, so I bought a set. I have never found that Iridium plugs were any better than a good 2X platinum, and this is not a daily driver, but if there is a problem with this I'd like to know before I install them.