If cortisol blood test came back normal, could salivary cortisol lab show diff? Dr is checking for adrenal fatigue.

It depends. This is serious business. The real question is, "Do you have Addison's disease?" A spot serum cortisol is often normal even in Addison's, making the diagnosis tricky. There are decision levels for the easy screens that your physician is aware of, but if there's any doubt, you'll probably get an ACTH stimulation test. Avoid "pop"/"fad" diagnoses like "HPA axis fatigue". Best wishes.