An interesting problem...
Does it extract white box Wal-Mart ammo OK???
Does the primer on the fired cartridges look "flattened"???
It sounds like the chamber pressure is still high and the shell is still sealing the breech while the extractor is trying to pull it out...I would guess slow burning powder, probably too much...
The pressure should be high when the powder is first ignited, the shell will expand to seal that end of the barrel; then it should fall as the bullet reaches the end of the barrel...the extraction sequence should have commenced before then...When the pressure has dropped...
That's all guesses, of course...(and a gross over-simplification)...It could be a simple problem like crud under the extractor...
I reload a lot, and tune my reloads to the individual weapon...I carry a brass squib rod and a little brass mallet with me to the range...I field strip my pistol completely when I hear a strange report when firing...I've found that other shooters get nervous when they see me tapping the rod down the barrel... 