I'll tell you what's wrong.....
You have a ford truck with a manual tranny. That's why it won't disengage. The clutch mechanics are a joke on these trucks. Second only in worthlessness to the clutch hydraulics.
The only thing you can do without buying anything... is to pull the slave cylinder out of the bellhousing and slowly cycle the shaft all the way in the cylinder and then let it push it's self back out again. Repeat that about 4 or 5 times and try it. If it's still not good enough do it more, up to 5 more times. But be aware that if you get carried away, #1, you might not be able to get it back in the tranny because of the pre-load needed to push it back in there, and #2 if you're making decent power you might slip the clutch because the throwout bearing may be applying pressure to the diaphram even without you touching the pedal.
So, just try about 5 cycles.
To get the slave out do NOT remove the line. Simply grab it on that big molded plastic nut and while pushing it toward the front of the truck, simultaneously rotate it counter clockwise (left) and it will snap out. Be aware that the rod leaving the slave will likely have a little plastic dickfore hanging off the end of it to try and snag on the bellhousing and pull the rod out of the slave and drop it in the bottom of the hellhousing. Avoid this.
To put it back in, just do the opposite of the removal.
Buy a new master/slave assembly from Ford for around 130 to 150 or so bucks. If you do this, be sure to also buy a new actuator rod that goes from the clutch pedal to the master cylinder as well as the little pos plastic snap bushing that is used to hold the rod to the pedal as it will be worn out/destroyed by your removal method. Alternatively you can choose to not purchase a new pedal actuator rod and instead take a hammer and smash hell out of the old master cylinder releasing the rod from it to reuse. Choice is yours. I personally enjoy beating hell out of the plastic junk and reusing the rod.
To remove the master cylinder...
Lay on the floor of the truck, looking up under the dash with the driver's seat all the way back for room. With a flashlight and a small screwdriver pop the little cover off of the clutch saftey switch (this switch will be against the master cylinder at the firewall, but will move toward the pedal if pushed away to get more room). With the cover off, it will pop off of the rod and hang freely. Then pry the rod off of the little stud on the clutch pedal leaving the rod hanging out of the mastercylinder.
At this point go around to the underhood area and grab hold of the master cylinder and rotate it similar to how you do the slave out of the tranny bellhosing. I do not remember the direction of rotation off hand, but it will only go one way. Do NOT worry about breaking the pos. It will likely take some serious force. Sometimes not, but sometimes it does.
Once you have it free, pry the little plastic "trees" that hold the reservoir to the harness cover out near the cowl. Be very carefull not to break this thing. It's very delicate.
Route the little reservoir and line down toward the frame so that the master and the reservoir/line are all shoved down near the back of the engine or simply hanging down past the frame.
Then go under the truck and pop the line out of a few of those little pastic snap holders along the body.
That's it. It's out of your life.
To reinstall the new one...
Install the slave cylinder into the bellhousing by pushing forward and twisting to the right until it clicks in place. LEAVE the plastic strap on the rod. It will break when you mash the pedal the first time, but serves to keep the rod from falling off in the meantime.
Resnap the line into all the little clips along the underside of the body and shove the master/slave up on top of the frame rail or inner-fender so that you can grab them from above.
Go up top and grab them and route the master over to it's hole and install by pushing toward the firewall and twisting opposite of the direction you removed it in until it clicks in place.
Then route the reservoir up to it's little tab on the wire harness cover and reinstall the little plastic "trees" on each side taking care not to break the delicate little flower of a plastic tab...
Go inside the truck and do N O T clip the new actuator rod and plastic bushing onto the pedal yet. First push it into the master cylinder otherwise you may not be able to move the pedal far enough back to facilitate getting the rod into the master.
With the end opposite the loop in the rod pushed into the master, install the little plastic bushing into the rod loop and push both the rod and bushing together over the stud on the pedal until they snap in place. Remember to reinstall the clutch safetey switch by slipping it over the rod and snapping the cover back on. It is sometimes useful to rotate the switch around the rod to make removing and resnapping the cover easier.
Now sit in the seat and push the pedal down. You should feel the rod snap into the master cylinder and the little strap pop off of the rod in the slave cylinder in the bellhousing.
Alternatively you could install the master and reservoir and drop the slave down from the top. But the wicked ass bends in the line like to fight you. I've done it each way about 4 or 5 times, so it's a toss up.
Oh, third option. Get a non-stock clutch that has better diaphram leverages. I can recommend a guy if you like. Otherwise, Southbend seems to be the mass supplier.
HOLY HELL that got long.