Auto Stag - Pressure Loss

[PGAHOWELLS <PGAHOWELLS@domain.elided>]

Hi all
I asked about the following a while back.
At cruising speeds a little over 3500 rpm, my autobox will lose all the
pressure, and the engine flys away to 5500, while I slow down. Five seconds
later I am back to normal, although sometimes I get a permanent selection of
second, and slow right down then the top gear will come back.

Two days ago I accidentally overfilled my auto transmission with fluid. It was
starting to fill up the fill tube. (I thought it needed more than it did. It
leaks a bit!)  
As a result of this over fill the loss of pressure at 3500 rpm did not happen.
It did happen much later in my trip than usual and at a much higher speed
(4500) and going uphill. The pump runs out of fluid. 

Has anybody got any ideas. Is my dipstick too long? (OK,OK you know what I
mean). What level of fluid has to be in the transmission in order for the pump
to pick it up. Could the pump have a tube missing off the bottom, or a spacer
off the top, and be mounted too high?

Peter Howells
Still puzzled by this one.