First your spindle speed is too low. We run at S1400 in the same material with Seco CP500 lay-down. You might be able to run even faster with the Sandvik insert. Second I think your D value is a bit large. Start at D.03 and experiment from there. The regular Okuma programmer used D.016, but I consider that too light for this coarse a thread. I normally stick with U.006 for 316 SS. Need to keep material from work-hardening.
I prefer M32M75 with B around 50, but I am more use to Fanuc controls.
EDIT: You can alway increase the H value and keep the D value a little bigger in order to keep the number of passes down. That way the first cut isn't as heavy yet the number of passes doesn't increase as much as they do when you drop the D value.