When I was on prednisone alone I could never get down to 5 mg let alone taper any lower than that.

I tapered that quickly when a biologic called Actemra (tocilizumab) was tried. I tapered my prednisone dose by 1 mg per week when I was doing Actemra injection so yes tapering that quickly is possible.

I had to stop tapering when I reached 3 mg of prednisone because of a low cortisol level.
https://www.endocrine-abstracts.org/ea/0056/ea0056p44
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When my cortisol level improved, an endocrinologist said I could go from 3 mg to zero without tapering. My endocrinologist said no tapering was necessary at that low of a dose as long as my cortisol level was adequate.

I suspect faster tapering while on low doses of prednisone depends on your adrenal function. This assumes PMR is in remission. Kevzara might help to get PMR into remission but it doesn't come with any guarantees.

Why are you resistant to Kevzara?