Wants to be sluggish, first to last (5)
I believe the answer is:
lacks
'wants' is the definition.
('lack' can be a synonym of 'want')
I can't explain the remainder of the clue.
(Other definitions for lacks that I've seen before include "Needs" , "Wants, is deficient in" , "Doesn't have" , "Has a want" , "Is without, wants" .)