I think United should stick to 352 formation, playing 3 at the back we looked more assured. Dropping Lukaku needs to be done. I would go with this line up.
DDG
Lindeloff--------Mike------------Jones
Valencia-------------Afro----------Matic-------------Young
Lingaard
Rashford------------Martial
Playing Rashers and Martial both up front where they both want to play could help them develop better and maybe get a combo going. Lingaard has been really good for the last few games hence starts, otherwise Mikhi/Mata, or even Pogs to play there to encourage him to get more involved in the attacking side of the game. Lukaku needs to be dropped, he has not been poor but abysmal. Except for that goal against Southampton, he has not scored any match winners, United bought him for 75 mill to win us matches, not to score only when everyone on the team is scoring or when we are comfortably winning.