99' Missing problem

Vehical: 1999 Chevy Silverado Z71 4x4 Extended cab,. 5.3 liter automatic with 143k miles.
I've had this truck for almost two years now and it had 89k miles on it when
I bought it. I'm about to (if I can afford it) replace the plugs, wires, and at the very least both pre cat O2 sensors here pretty quick because I have no idea when the last time any of these part were changed and I'm sure someare original.....
I've always had a problem with the motor missing when it's hot out but it's not limited to just when it's hot sometime it'll do it cold but it's certinally worse when the weather is hot and the truck has been driven for wahile. I normally run regular unleaded (86 octane) and have tried running a tank of 89 octane through her and nothing really seemed to change.
The check engine light has come on several times since I bought it but it always either goes off by itself over time or can be reset wtih a scan tool and it wont come on for another extended period.. The only code I can remember pulling are knock/miss codes, you'll have to excuse me I can't remember the code number off the top of my head.
Besides the fact that I want and really need to change these parts anyway does anyone have any ideas what else I need to look at? What about the knock sensor itself? I honestly think that the O2 sensors are the biggest part of my problem next with plugs and wires.
Suggestions Welcome before I go spending money I don't have! :)
Adair
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The plugs and misfire are usually connected at that mileage, look at the rotor and cap too, fuel filter, clean the maf with electical parts cleaner.

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Thanks for the info.. There are no cap and rotor on these trucks they have a seperate coil for each plug. the fuel filter has been replaced recently with a wix. The MAF brings up an interesting point. This truck had a K&N filter in it when I bought it.. I bought a cleaning kit once and cleaned it.. then after reading up on how crappy they are I changed to the Wix HD air filter.. I was worried that either I or the people before me might have over oiled the filter so I removed the MAF and cleaned it with cleaner. What are the odds that either being of being dirty OR from cleaning that the MAF is causing problems also? I also forgot to mention that at time at high RPM the motor will backfire into the exhaust.
Adair.
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What is high rpm, this has an rpm limiter especially in neutral. MAF is probably ok, with no cel on. Forgot 99 had direct coil ignition, make sure you use oe Delco plats or the new Iridium plugs.
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high as in to 4k and over. i've only ever had it to do it while driving.. say doing 70 and start up a grade and it shifts out of over drive and brings the rpm up high
I was planning on using ACDelco Platinums.. not sure what the other ones are you are talkin about.
Adair
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