I use a .125” T shaped HSS tool and holder from Shars. I leave it about 1” out, I don’t adjust it for the part diameter. I part steel at 90 rpm, aluminum at 250. Both with the feed set at approx .010” / rev, so an actual feed of about .005” / rev. Lathe is a 1440GT.
I have parted 303, 304, 6061, 316, 416, 4140, brass, UHMW, and mystery metal, in diameters up to 2”. I always use power feed.
I have never had a single problem. I’m not an old hand, but I’ve made several hundred parting cuts, I’d estimate 300-500.
I sharpen the tool when it no longer feels quite as sharp, maybe 4 times now.
Perhaps my time is coming, but all the parting woes are a little mysterious to me.