I've been working on a 3 day split for the past few months and i really enjoy it compared to my 5 day split before and have noticed great size gains. Should i add shoulders to legs day? i couldn't possibly add them to any other day as i already spend a lot of time in the gym working out two body parts a day.

Day1 chest and tris
Day2 Back and bis
Day3 legs (and shoulders?)
Day4 rest