Also make sure that the mechanical system doesn’t have any “slop” in it. Check things like the grub screws that hold pulleys to motor shafts, etc.
If the mechanical and steps per mm check out all right, the next thing to look into is the universe of variables that govern the amount of plastic being extruded. Once the current mechanical checks are completed I can provide a pointer to a process for fine tuning E steps per mm, temperature, and extrusion multiplier settings.