The same as the converter is the same. Rear gear doesn't impact stall, that's strictly the convertor and to a lesser degree cam timing. The flash rpm of the convertor may be a bit lower with a 3:92 gear because part of what creates the stall is converter load and a 3:92 gear will put slightly less load on the convertor than a 3:21 would, so a slightly lower flash rpm vs a 3:21 gear.
Converter flash is that couple extra hundred RPM that you see after the initial stall speed when you release the brake. To easier see converter flash, stall out the truck with the foot brake and note the rpm that creep starts, now release the brake and watch the tach jump a 2-300 rpm more before the vehicle moves.
Another way to see flash is to not load the converter, keep your foot lightly on the brake and the other touching the accelerator pedal but not applying pressure, no stall.
When the light changes (obviously do this in a no traffic area) release the brake and go WOT on the accelerator while watching the tach and you'll see that it "flashes" to a higher rpm before the vehicles starts to move.