RE: Spark Plug replacement 99 5.7L ?
I am a long time fan of NGK plugs and have used them in my '99 Suburban but there are some things that I have learned. I replaced the original AC-Delcos at about 103,000 miles with NGK 3403 (TR55GP) platinum plugs. These are fine-wire, single platinum style plugs. They lasted about 30,000 miles and gave good performance until they began to fail. They cost about $2.29 from O'Reilly. I replaced the 3403's with NGK 1465's (IZTR5B-11) which are fine-wire, Iridium - platinum plugs. They cost about $9.49 each from O'Reilly. I was hoping that these would last as long as the OE plugs did. Unfortunately they were only good for about 35,000 miles. It is interesting to note that though the NGK lists the 1465's for '99 Suburbans, O'Reilly does not. I still believe that NGK makes great spark plugs, but that the fine-wire construction (intended to reduce ignition voltage requirements and provide more exposure to the fuel charge) results in faster erosion than more conventional construction styles. Therefore, if you are planning to keep the vehicle for several more years I would have to recommend the AC-Delco 41-993, double platinum (not fine wire). They cost $5.99 each at O'Reilly. If you want a shorter life, lower cost plug, I would use the NGK 3403's.
Also, if you have over 100,000 miles on the Suburban and have not replaced the distributor cap, rotor and spark plug wires, you should do so. I recommend Magnecore or NGK wires.