Nozzle diameter (too big)
Retraction (is motor skipping -listen for beeps on retracts. If so, slow retraction speed or lower retraction acceleration in EEPROM until beeping stops.
Extra filament after retract
Extra filament in tool change
Extrusion multiplier (in your slicer)
Line width and height.
And only because I know you’ll probably do it : Linear Advance. (You’ll need to enable it in firmware first). Post a new thread if you’d like help with that.
Let me know if any of this helps. If not I’ll help you get to the bottom of it.