Slow vehicle from old times superior to, say, Tesla model (6)
I believe the answer is:
oxcart
'slow vehicle' is the definition.
'old times superior to say tesla model' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'times' becomes 'x' (multiplication sign).
'superior to' says to put letters next to each other (in a down clue, some letters go above others).
'say tesla' becomes 'car' (Tesla is a car manufacturer).
'model' becomes 't' (Ford Model T car).
'o'+'x'+'car'+'t'='OXCART'
'from' acts as a link.
(Other definitions for oxcart that I've seen before include "Animal-powered vehicle" , "Vehicle drawn by a bullock" , "Neat transport" , "Primitive rural transport" .)