I had a customer bring a big cam 350 and auto trans 70's chevy to me, complaining about stalling. He had jacked the idle speed to 1300rpms to try to remedy this, to no avail.
I adjusted the idle to about 700 and the problem went away.... at higher idle rpms the converter is not locked or engaged but the fluid is "flashing" the internal parts when it should not be doing anything, and t makes the converter try to grab. "Flashing" may be the wrong term here, not sure. Splashing may be more accurate.
Anyway, I know it sounds backwards, but LOWER your idle to where it belongs. See what happens. Lower idle will not splash fluid so much in the converter and cause resistance.