New Slave Cylinder won’t compress, is it faulty?
 

I just got done replacing the whole clutch system in my 2001 4.0 4x4 Ranger I got a few months ago. As me and a buddy were putting the tranny back in it wouldn’t slide in. We used a crowbar and eventually got the bolts to grab the threads in the transmission and sucked it down the rest of the way. Now that I’m looking in through a vent hole in the tranny I see the springs all the way compressed in the pressure plate. The slave cylinder / throw out bearing is still up all the way. I don’t know anything about trucks but I’m assuming it should be compressing under that weight? What do I do?

Hydraulics don't compress. The fluid must have a place to flow. I am guessing you did not connect the slave line to the master cylinder line, and you probably will not be able to until you open the bleeder to release the pressure in the slave, which will also release the tension in the pressure plate.