Stumbles over a stone finally in trek (7)
I believe the answer is:
traipse
'trek' is the definition.
(both can mean to walk sluggishly)
'stumbles over a stone finally' is the wordplay.
'stumbles' becomes 'trips' ('trip' can be a synonym of 'stumble').
'over' means one lot of letters goes inside another.
'finally' indicates one should take the final letters.
The last letter of 'stone' is 'e'.
'trips' enclosing 'a' is 'traips'.
'traips'+'e'='TRAIPSE'
'in' acts as a link.
(Other definitions for traipse that I've seen before include "travel wearily" , "Parties (anag.)" , "long tiring walk" , "Walk heavily" , "Tedious walk" .)