Did you experience any symptoms of adrenal insufficiency?

Adrenal suppression is probably inevitable with any dose of Prednisone. However, adrenal suppression is only temporary for most people. I was told that 12 years on Prednisone was a long time but as long as my adrenals were able to produce cortisol again then my cortisol level would improve with time. Some people have adrenals that are permanently damaged and incapable of producing cortisol again.

I can only guess at my cumulative dose of Prednisone spread over 12 years. It was probably in the neighborhood of 100,000 mg. I probably averaged 30 mg per day for 5 years. Then an average of 20 mg per day for another 5 years. Finally 10 mg per day for the last 2 years just for PMR alone.

That doesn't count the many times before PMR was diagnosed. For other autoimmune conditions, I took upwards of 100 mg per day but tapered off in a month or two. People have many misconceptions about Prednisone tapering and how much Prednisone is needed. It really depends on the condition being treated. How long the condition is treated makes a difference in how long it takes to taper off. The problem with tapering off Prednisone stems mostly from HPA axis suppression.

The guidelines from endocrinologists say the following:

"R 2.1 We suggest not to taper glucocorticoids in patients on short-term glucocorticoid therapy of < 3-4 weeks, irrespective of the dose. In these cases, glucocorticoids can be stopped without testing due to low concern for HPA axis suppression."
https://www.endocrine.org/clinical-practice-guidelines/glucocorticoid-induced-adrenal-insufficiency
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What surprised me the most was when my endocrinologist said 3 mg was such a small dose that there was no need to taper. The justification she used was that my cortisol level was adequate and PMR was controlled. The thing that worried me was my endocrinologist didn't know what would happen if I stopped taking Prednisone.