Liverpool have really struggled to win their last few games in the Premier League, but when they play Manchester United I'm sure their performance will be better. Liverpool's performance is very good and they are working according to what Klopp expected, so 37 points in 16 matches is enough to prove they are superior to Manchester United.
Liverpool has strong games coming which they should be prepared for, against Manchester United then against Arsenal. Those two games will determine if Liverpool will remain in top of the table or not, I bet that is the reason behind the coach resting some major players in his team like Mo Salah. After Manchester United, Arsenal will be ready because they have a great team news about the return of Thomas Partey who is an important player for Arsenal especially against other big teams because of his versatility.
You are right, it's easy to guess Liverpool really prepared the main player for these 2 matches because the results of the match will determine their position in the standings. Currently Liverpool are 1 point ahead of Arsenal, meaning they can't miss a single point even a draw will have an impact, fortunately all important matches at the end of the coming month will be played at home so Liverpool have a great chance to win.