The six-cylinder models had a master/slave cylinder on the clutch. What model do you have?

The symptoms you describe are those of the clutch not disengaging. There are several possibilities for that failure. Clutch cables stretch and/or break, and the arm holding the throwout bearing can bend. BTDT on all that.

Do you have a tach? It makes it much easier when driving without the clutch. It's an old/lost skill, sort of like double clutching. Requires that the engine speed relation to road speed be such that the gears are not under load when it's time to shift. Works in either up-shift or down. Only problem is at a complete stop. In that case it's necessary to turn the ignition off, and then start the engine in 1st gear when moving out. I had to re-learn all that when a clutch cable failed in heavy traffic 10 miles from home.

Good Luck,

Bob

:>)