Welcome to the forum!

Sounds like you are taking good care of your new family member. I love to see people do lots of research before buying a frog instead of just getting one improptu.

I couldn't tell you for sure, but in my personal experience the open and close mouth thing is what mine did when he was really hungry, after he swallowed something (like cocofiber or a cricket), or when he was too hot. You mentioned a temp of 90, which is abit hot for Pacman Frogs. If you can take it down afew degrees (80-85 is prefered during the day) then your Pacman Frog would appreciate it, but I understand that it can be hard to get temps down (believe me, living in Texas, I know).

If you need any additional information you can always ask. The forum also has a Pacman Frog Care Article.

Either way, welcome to the forum!