Flash o matic question

I have recently bought a 63 Rambler with the flash o matic box in it, after driving it and finding it slipping in gear I dropped the sump to hind the tv cable end broken so I repaired and all good.
My question is when in drive and cruising, when you lift off the throttle, the revs stay as in gear, and not drop to idle like most other autoboxs I'm used to, is that normal for this box?
Cheers

With the carb at idle position set the length of the cable so that it has a "loose pin fit" -- the pin that holds the clevis to the throttle linkage easily slides in/out. Then lengthen the cable by two turns. That is the factory setting. You can increase/decrease about 1 turn to tweak shifting. Increasing length increases pressure in the trans and firms shifting a bit. If you go over about 1.5 turns over stock you will find the trans downshifting a lot sooner also, sometimes when just maintaining speed up a hill when it's not necessary to down-shift. The cable also serves as a kick-down. The trans will down-shift when the cable "bottoms out" and road speed is under 60 or so.

As Tom mentioned, driving without the cable attached can burn the trans up because it slips to much. I wouldn't shorten the cable at all, as that reduces internal pressure. The reason for this is to allow easy shifts but still maintain adequate holding pressure as power (throttle) increases. A vacuum modulator does the same thing, only uses engine vacuum instead of a cable (open throttle = low vacuum).

automatic transmissions do not freewheel. under certain conditions planetary (manual) overdrives do. you may be thinking of the inherent "looseness" in the torque converter coupling.