2004 Silverado 5.3l Stumbles at idle, no fault codes

[Jager311]

I have a stumble only at idle or when first accelerating from a stop, the engine rpm will stay around 500 then dip for a second to maybe 300-400 it isn't consistent and sometimes feels worse than others, you can feel a slight stumble when you first leave a stop but after that it's fine, smooth and no lack of power. The MAF and throttle body have both been cleaned properly but neither made any difference. The engine has about 205k on it, the plugs have about 80k on them now. I'm not sure where to look next ?

[Brian715]

I sometimes track misfires and whatnot with an ELM327 wifi OBD2 scanner and the torque pro app on my phone. You can see live data of a lot of sensors and help narrow down the issue. 500 RPM seems a little low, I think my 06 idles around 600 or so. No aftermarket cam or anything? 

[Jager311]

 No cam, completely stock.