1996 K2500 Sub L29 454 Hesitation off idle

[inconceivablemotors]

Has anyone ever found the reason for the stumble off idle?
The engine fully warmed up, at idle 650rpm, at a stop... then press the gas pedal to start moving and the engine will surge / hesitate, then jump up to about 900 RPM and the truck drives perfectly normal from there.

Live data all looks good, timing is correct, did a smoke test no vacuum leaks. So far I have replaced:
-Intake gaskets
-Fuel injectors and regulator
-Fuel pump
-Distributor, wires and plugs
-Idle control valve - It seemed lazy
-Timing chain and sprockets
-Crankshaft sensor
-O2 Sensors

And so far have not been able to resolve this..... Any inside greatly appreciated.

 

[Keeper]

I think I read something by @L31MaxExpress where he said that it is part of the stock tune. It's annoying though, for sure.