Could the snake have taken a drink of water before you saw the "drool?" Sometimes they'll let water dribble out of their mouths. If you only saw it one time and no other, along with no other symptoms...it could have been something as simple as that.

It does sound like the enclosure needs to be tweaked some, though. You need to get better control over the temps. 90-100 is too hot and too wide a range...the warm side should be 90-94....and the cool side should be 80-84...and those temps need to be maintained 24/7. Make sure the enclosure is not near anything drafty like a window or door. I cover my enclosure with a thin blanket at night to help keep the night time temps stable...as well as closing up the room its in so its not drafty and all the warmth thats in there stays there. If your enclosure is in a huge open space (like a living room or something) you may need to consider moving it to a small room where you have better control over the ambient temps.

Also...you should have two hides (preferably identical) at a minimum. One on the warm side and one on the cool....that way the snake never has to choose between proper temps and security. If floor-space is an issue, ditch the large water bowl and go smaller...they don't need to soak.

If you truly suspect an RI...bump the temps a couple degrees from what I've already mentioned...and go ahead and make that vet appointment. Only a vet can determine for sure, and IF the snake has an RI, it will require medical intervention.

Good luck with it!