Worth yours truly slowing down (5)
I believe the answer is:
merit
'worth' is the definition.
(merit is a kind of worth)
'yours truly slowing down' is the wordplay.
'yours truly' becomes 'me'.
'slowing down' becomes 'rit' (I've seen this in other clues).
'me'+'rit'='MERIT'
(Other definitions for merit that I've seen before include "Have a right" , "credit" , "Excellence, worth" , "Excellence that deserves to be honoured" , "Good point or quality" .)