Rangers use an internal slave cylinder so there is no external adjustment.
They also came with a self-adjusting Pressure plate which will keep the engage/disengage just below center travel of pedal.
Yes, air in the system will cause your symptom.
Hydraulic fluid doesn't compress under pressure, air does.
If there is even a little air in the system when you push in the pedal the air compresses and the slave doesn't push out all the way, so clutch engage and disengage is right at the floor.
Make sure clutch reservoir is full and then bleed the system, if this doesn't get pedal back to normal, this is a video on how to bleed Master in the truck:
https://www.youtube.com/watch?v=Pd1KDCAhTLc