2000 5.3 rough idle when warm

[busta]

i have a 2000 silverado with 5,3 115000km i was feeling rough idle while say in coffee line up the rpm will surge/drip/drop a little then return .nothing major but really bugging me so i changed my plug's to plat. plus 4 plugs and wire's and still the same thing, i put some stp fuel injector cleaner thru it and will continue to use every oil change(could it be dirty injector's?)i dont know i think ill pick your brain before i start changing part's)i.e tune up p.s no code's so could it be lazy co2 sensor,
dirty injectors,gummed intake,maf dirty,i.a.c????? thanks need somewhere to start. the engine is stock and havent really done much to it since new . later.