I'm just saying there's a huge, noticeable difference between the way Caroline and GLaDOS act. I didn't even make the connection that Caroline was possibly human GLaDOS, until GLaDOS herself mentioned it in the game. If GLaDOS wasn't a sarcastic, bitter science fiend as a human like she is in both games as her AI self, then something happened to piss her off.
Another thing I was thinking was that one of the reasons GLaDOS tried to kill the staff when she was first awakened was because Caroline didn't want to be brought back. If Cave Johnson was her husband, the last thing she probably wanted was to be brought back to an eternal existence without him. Maybe the Solution Euphoria was a way for the staff to pacify her. It was probably also the closest thing she'd experience to love in her new body. After a while, she probably became addicted to it, and that's probably where her constant need to test came from. She was trying to fill some sort of void. What doesn't make sense, though, is why she killed everyone when she needed them to fill that void. The reason I doubt that GLaDOS was always and only in it for the science is that Caroline kind of comes off as just a bubbly, air-headed assistant, nothing like the GLaDOS we know and love. She doesn't seem that interested in science, either. The Half Life Wiki also says that the GLaDOS personality formed while Caroline was in her new body, due to constant testing. Eventually that personality took over, and Caroline was shoved aside. It kind of makes me think that GLaDOS was some sort of coping mechanism that just went out of control. Maybe GLaDOS formed shortly after Caroline had built up a resistance to the Solution Euphoria in order to cope with not feeling that "love" anymore, and helped her direct her attention to a new love: science. That's kind of my head canon. Don't know if any of it's true, but that's the impression I got.