2000 Silverado 5.3 misfire

[76stepsidechevy]

I picked up this 2000 Silverado with a 5.3 about 6 months ago needing some tlc. It ran good but had a slight miss at idle. Then a week into driving it it started throwing a cyl 6 misfire code. I swapped plugs and wires and coils but it still set the code for cyl 6. I ended up throwing a set of plugs and wires at it as well as a new coil pack on cyl 6 out of frustration. It runs a lot better since then and the miss at idle seems to be gone but I'm still getting the misfire code. It will stay off for a few days and will go off by itself eventually. It seems to only set the code when warming up from a cold start at idle. I can drive it all day and never set the code. I'm kind of at a loss here since it runs well. Where do I look next? Injector ? Intake gasket?