@jeff97 -- Thanks for taking the time to reply with this reassuring report of your experience. With the exception of this jaw pain, which I feel when eating (sometimes) and brushing my teeth (always), I've been feeling quite well on the diminishing dose of prednisone and actemra infusions. Because the jaw pain was the main GCA symptom, it does trigger some concern; but I have to say that I've been having this pain for many months, even when I was on the high doses of prednisone. I was also diagnosed with Lyme disease last fall (result of a blood test done by my rheumatologist when I was first worked up for the GCA/PMR) and given antibiotics. Though I hadn't hadn't noticed any symptoms related to that, I did read that Lyme can cause jaw pain. It was all part of a very confusing picture at the time.
My rational brain agrees with you that this is likely TMJ related pain, and it does help to have your perspective to fortify me when anxieties arise.