Driving down interstate at 70 mph car suddenly

pcm problem take it to dealer

have the fault codes read by a service center that knows how to turn on the nissan ECM
it goes into limp mode from a sensor reacting to a serious engine or transmission fault
unlikely that it could be a throttle body as that is not a sensor that would normally cause limp mode

On GM cars this type of problem was a sticking torque converter. The car acted like you had not engaged the clutch and the engine just died. You could restart it and drive on as long as it did not go into lockup.
Does it feel like that, or more like the idle air control valve is not raising the idle speed ?

Thermostat goin out

check those codes sounds like a torque lockup solenoid

No....the rpms differ from engine to engine and from manufacturer to manufacturer. RPM's are always higher at higher speeds.

THrottle position sensor check that.

You need to have it scanned. The od off light is like the check engine light for the transmission. It will flash when you have transmission codes.

Nita0605 you should have included a little more infomation. Does the car drive any different when the light is on? Most likely you have a trouble code P0325.........Knock sensor fault or O2 sensor problem. I wouldn't worry about it until the light stays on

check your throttle position sensor