Shifting problem

Could be air in the system, the slave cylinder or a worn out clutch. Or depending on exactly what the shifting issue is it could be internal transmission mission wear.

That truck has an integral slave cylinder. It can be difficult to bleed it correctly. The process uses a mity-vac or similar pump to apply a vacuum to the reservoir on top. You fill the reservoir and apply vacuum until you stop seeing air bubbles.

Trouble shooting is basically does the clutch release fully while setting still and while driving with no slipping while engaged.

What is the exact issue you are having while shifting?

So you can push the pedal down and it may/may not disengage. That could easily be air in the system. I would start by bleeding it using vacuum.
If you get no improvement then you will probably end up pulling the transmission. They are not real hard to do. I would opt to install a clutch kit at the same time.

The basics are,
Inside the truck you shift into fourth, then remove the shift tower.
Get the truck up enough that you can get under it.
Remove the exhaust.
Drain the trans fluid
Remove the drive shaft.
Remove the braces that go from the trans to the engine.
Remove the wiring harness from the trans.
Disconnect the clutch cylinder line.
Remove the clutch cover.
Support the transmission with a transmission jack.
Remove the transmission crossmember.
Lower the transmission about an inch and remove all of the bell-housing bolts.
Pull the transmission straight back until it is out of the clutch plate.
Lower the transmission and pull it from under the vehicle.

Reverse the process to put it back.