The current routine I have is;

Chest/Shoulder/Tri

Legs/Back/Bi

I tried to get the gym 4 times a week all on weekdays and have 2 on 1 off. If I go through a period of only getting to the gym 3 times a week I alternate which day I do twice that week. Anyway what I am asking if something like this would be better or stick to my current routine.

Chest/Tri/Cardio

Legs/Back

Shoulder/Bi/Cardio

Because I noticed one day last week when I concentrated a day solely on shoulder and Bi that I could lift 15lb more than doing it after my chest. Am I short changing my shoulders or not? Also this way there is no mix and matching the excerises as would only need 3 times a week.