Questions regarding 3l80 Transmissons and down shifting

[AOR]

I am a new to owning a HMMWV. I have a 1986 with the 3L80 3 speed setup. Should it downshift on its own when pressing the accelerator down to the floor and at what speeds would it downshift?
Also there is a cable that connects onto the passenger side that has a minor leak does anyone know exactly what it is for? I have been told very different things from people who deal with these every day.

 

[2wheels70]

A 3l80 or turbo 400 should downshift if you press the accelerator to the floor and you're going slow enough to require the lower gear

 

[dhaumann69166]

The turbo 400 will downshift but you have to be lugging around at pretty low RPM and put it all the way to the floor. I usually shift manually when driving mine just to keep better control of the RPM and not make it lug around so low. The only time I have had mine kick down a gear is starting into a soft sand hill climb and usually I try to have it in the desired gear before starting into the obstacle. 6.2 is a low RPM motor so don’t expect it to grab a gear and rap up hard like modern vehicles. Also when you put it flat to the floor your clutch fan should shut off for 30 seconds.