Firmware retraction is slow moving, slicer or klipper problem?

A klippy.log would help since it contains the interpreted config that you are using. You either can zip it, upload it to gdrive.

The settings that limit retraction velocity are:

[extruder]
#max_extrude_only_velocity:
#max_extrude_only_accel:
#   Maximum velocity (in mm/s) and acceleration (in mm/s^2) of the
#   extruder motor for retractions and extrude-only moves. These
#   settings do not have any impact on normal printing moves. If not
#   specified then they are calculated to match the limit an XY
#   printing move with a cross section of 4.0*nozzle_diameter^2 would
#   have.

And if you are using firmware retraction (G10/G11):

[firmware_retraction]
#retract_length: 0
#   The length of filament (in mm) to retract when G10 is activated,
#   and to unretract when G11 is activated (but see
#   unretract_extra_length below). The default is 0 mm.
#retract_speed: 20
#   The speed of retraction, in mm/s. The default is 20 mm/s.
#unretract_speed: 10
#   The speed of unretraction, in mm/s. The default is 10 mm/s.