I am 3 days post-op. Today is my first day of full liquids. Had a protein shake for breakfast sipping slowly over the course of an hour and it went fine. Tried again at lunchtime and had major diarrhea. Does that mean I drank too fast or had too much? No nausea. I am confused about how much liquid to take in- worried about dehydration but also don't want to overdo it.

Pretty much. Liquid in, liquid out! Poo isn't going to become more solid until you are on something more solid.

As for too much or too fast.. sounds like you are sipping and being compliant.

I was that way until I started pureed foods. Now I'm wondering when I'm going to go....

Enjoy it while it lasts because after surgery there is a good chance you won't go as often as you do now. It sucks!