flybubba,
An addendum to my previous post. I stated for the example given "a drag increase of 6.3% between 25943 ft and 10000 ft", true. I then went on to say that for practical purposes the descent gradient can be considered as fairly constant. This seems a little too simplified in view of a 6.3% increase in drag, which would lead to a noticeably steepening gradient. The addendum (fancy way to say this is what I forgot to say) is that TAS and therefore momentum is decreasing during the CAS phase, and the kinetic energy is dissipated as an effective increase in thrust, thus lessening, but NOT cancelling the overall effect of a steepening descent. This is, in fact, the opposite to climb at a constant CAS where some of the available thrust is used to accelerate the aircraft, leading to less being available for climb.
Hope that this does not add to the confusion.
Regards,
Old Smokey