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?

[99LS1500]

Which code is it throwing ?

[76stepsidechevy]

It's P0306

[76stepsidechevy]

It seems to only happen when the truck is warming up at idle for more than a minute or so. I generally let it warm up for 5 or 10 mins in the morning and if I happen to be running a little late and head down the road before it sets the code it won't set a code at all.

[99LS1500]

Did you notice any oil on the #6 plug when you pulled it ?
Did you gap the new plug prior to installing it ?

Could be your #6 injector going bad

[76stepsidechevy]

The plugs looked clean just a little worn. I replaced them with Delco iridiums that were pregapped and all checked out within spec before I put them in. I'm thinking maybe that injector is hanging open slightly? The truck runs great and has plenty of power. That's why I'm kinda stumped here. Is it common practice to change all the injectors at once or should I just throw 1 at it. I believe the motor has 225k on it.

[99LS1500]

I would pop 1 in it for now to see if it solves the issue.