Gaping usually is their way of cooling down, like a dog panting. Mine do it on occasion, usually when sitting under the basking lights.
As far as body language, from my own observations, when they are pi$í off, they sway their bodies from side to side, the uro dance (not to be confused with the glass dance LOL). If they are demonstrating this behavior it is best to leave them alone.
Since you just got your uro, it is stressed at the moment. One thing I have found to be helpful is to always talk to them in a calm soothing voice, even if they are hidden. They will recognize your voice and hopefully associate it something pleasant in the future. Patience is what it takes, but always remember, uros are like people, each has its' own personality, so some will become more tame than others. I have very tame ones and others that will not run when they see you but are not happy to be picked up either. Others are like reptile versions of your dog, love to be petted, held and sit with you. Good luck.
Pam