Are you a Big-Rig Hypermiler ?...

[Rawze]

the rule of thumb for OOG (out of gear) is anything more than 1/4 - 1/2 mile, especially when the truck is heavy loaded.

OOG is more effective when your heavy vs. when your empty and light ... this factors in as well.

and no ... OOG is always more efficient than in being gear and off the throttle down a hill. The engine always consumes more energy slowing down the truck, than it does consuming the 18-20 mg/stroke idling when in neutral.

Its just matter of getting good at when to OOG ... and when not to go OOG for the benefits.