Idling in N vs D observations

[gone-ot]

...on the Cruze with automatics, the transmission actually "disconnects" (no torque converter action) at full stops to reduce engine load and thus save fuel.

...from the GM TechLine website:

Neutral Idle

The neutral idle feature of the automatic transmission saves on fuel by automatically shifting the vehicle into a neutral state when the vehicle comes to a stop and the brake pedal is depressed. It shifts back to gear as the brake pedal is released.

Neutral idle is activated when the brake pedal is depressed, and the vehicle speed, throttle position, and transmission temperature are within the calibration defined limits. The TCM will command Neutral Idle ON. The low and reverse clutch remains applied. The TCM reduces the pressure command to the 1234 PC Solenoid 5, which reduces the fluid pressure to the 1-2-3-4 clutch, allowing the clutch to slip. This reduces the torque converter clutch (TCC) slip speed, which, in turn, reduces the engine load and lowers fuel consumption.