I think, but again I could be wrong, that the balance between speed and throttle position determine the "load". If you are say, cruising at 40 mph, there is little load, but if you advance the pedal (try to accelerate the vehicle), then the load increases. It's controlled by a valve, I believe which "floats" back and forth in response to both speed and pedal position, but, below a certain speed, regardless of pedal position, a downshift is commanded and, above a certain speed, regardless of pedal an upshift is commanded.
But, as I understand it also, a WOT throttle overrides everything and shifting becomes controlled totally by RPM.
As far as what constitutes WOT, I don't know. It seems to be awfully close to the max deflection point though. I know if I let up just slightly in a WOT situation, the transmission downshifts. I'm sure someone on this forum can enlighten us (and probably tell us that all my earlier statements were wrong too).
- Jack