While i know a little about ret paladin i havent played ret since last season and i think that someone like @rethumtv would be much better at helping you with this question as he was much higher rated than i and i believe mains ret.
The best advice i can give you is to play the blade of wrath slow pvp talent ( forget the name ) and try to predict roll / torpedo and re apply slow the instant they use it or to be very quick about using horse > hoj to catch them off guard.
if you run at them all game with double steed unbound freesom and a basically spammable 70% slow you should be able to catch them at some point for sure but doing damage is more important and you shouldnt over commit if say they literally scoot the fck across the entire map before you connect