Clutch pedal does not disengage clutch in '91 Chevy pickup. Changed Master Cylinder, slave cylinder, and bled hydraulic line. Still not disengaging clutch.Maybe throwout bearing stuck? Or clutch fork?

Did you get all the air out of the hydraulic lines and master and slave cylinder, if not the clutch will not fully disengage and you can't go into gear. If this is the case have it vacuum bled.

as per your description problem not clutch since able to start in gear and drive without stall problem sounds more like a fuel delivery not the clutch

When I do clutch jobs. I replace the clutch package(comes with the slave) and the master cylinder also. Have the flywheel turned or replaced. Just a note. The clutch plate can be installed backwards. No matter how many times you bleed it, It won't work.

It's your hydraulic clutch system that probably isn't working. When you press the clutch pedal down, it causes the clutch master cylinder to put pressure in the line to the transmission's little "slave cylinder" that operates the clutch inside the transmission bell housing. This disengages the engine from the transmission so you can shift gears. It's probably not putting the slave cylinder to work by hydraulic pressure. The clutch master cylinder is mounted on the firewall, similar to the brake master cylinder, the clutch cylinder has a reservoir and you may need to add brake fluid to it. If it is dry, then you will need the system bled at the slave cylinder by a pro or someone who understands how. Pretty simple, really, just like bleeding brakes. Also the clutch master cylinder can develop internal leaks and this will lead to loss of clutch.

You probably have a hydraulic clutch. A hydraulic clutch has both a master and a slave cylinder. The slave cylinder engages/disengages the clutch plate. You might be low on clutch fluid in the master cylinder, or the system may need to bled similar to bleeding brakes. Worst case is you need a new clutch, pressure plate, and throwout bearing. They should all be replaced when doing a clutch job.

Your truck has a hydraulic clutch release system, you have a problem in it due to a leak in the slave or the master cylinder, The slave cylinder which is the one that leaks most often is inside the bell housing and it requires the ****** be removed to replace it.

The clutch is operated hydraulically, and there is no adjustment. If your problem is that the clutch will not disengage or is hard to disengage you may be low on fluid or have air in the line. There may be a leak either at the master cylinder or the clutch slave cylinder. Bleeding the slave cylinder may restore pedal pressure. If the problem is that the clutch engages high on the pedal the problem is likely a worn clutch disc.

Your truck has a hydraulic clutch , that works just like brakes. A master cylinder connected to the foot pedal sends fluid to a salve cylinder inside the bell housing. If there is any air in the lines , the slave cylinder will not move far enough to disengage the clutch. The lines can be bled of air bubbles much the same way a brake line can be bled. Hopefully this is the problem. A worn out Master cylinder is not too big of a job to replace , however , on your vehicle the slave cylinder is inside the bell housing of the transmission , and replacing it would require removal of the transmission. If you are not loosing fluid out the slave cylinder it is probably ok.

make sure fluid is full... then pump the pedal with it NOT RUNNING as many times really fast as you can.. try it after that, if it works then you need either a clutch MASTER cyliner and/or a SLAVE cylinder.. MOST likely being the slave cylinder. if the pumping action doesnt cause it to disengage then you have a burnt out clutch. The system is hydralic and takes regular DOT3 brake fluid in the small resevoir under the hood next to the brake master cylinder...
The slave cylinder being bad would mean you have to removed the transmission and install a new slave cylinder... thats the most common issue with those around that mileage...