Here'* something I found that I might try regarding the TCC dropping out so easily....

www.sonnax.com/bulletins/tech/T3-EL-197.pdf

This tech bulletin is not applicable to our cars...only Ford transmissions...

Whoops...... Sorry.

Although, I still wonder if it might be of some value. Until I saw that bulletin, I thought only about the Throttle Position Sensor as the computers Que that the driver might be demanding more power/pull..... However, could it be the the MAP sensor also plays a role in this part ? Additionally if something was allowing some sort of vacumn leak, like a worn-out upper intake manifold, or associated gaskets, could that affect how the shifting on gradual hills is performed ?