dynobo

Ok guys this is my thinking. I'm trying to keep this from being a 4 page article........
While driving in O/D at say 40mph ( I think below 40mph it is suppose to drop to lower gear) around maybe 12-1400 rpm I attempt to give it throttle and it does nothing (dead pedal). By releasing the pedal completely it automatically kicks out of LOCKUP MODE (converter) in the tranny and will respond normally. On the gas trucks when your engine fell below say 5in/mg manifold vacuum then it would automatically downshift from O/D into 3rd.
If I push my foot FIRMLY to the floor it will drop down to 2nd and run like a raped ape. But it for some reason will not downshift from O/D at 40-50mph unless it is firmly to the floor.

I remember with the old gasser (95' 1500 5.2) if you were at speed in O/D and either tapped the brake or completely released the acc. pedal that it would drop out of lockup mode momentarily. This is what my diesel is doing but, will not kick down unless you are PEDAL TO THE MEDAL. So my question is "What causes the down shift on the diesels?"
Also, if I hold it to the floor regardless of gear it will pull to about 27-2800rpm and then fall on it's face. Is this normal for a stock 24v?? Thanks........