Clutch adjustment or bad pressure plate?

[68gmsee]

You probably guessed right with the pressure plate. If you adjusted the clutch so that the pedal engages the throwout bearing 1-1/2 inches from the top and still won't disengage the clutch that generally indicates the pressure plate is either worn excessively or defective.

A worn clutch disc generally will manifest itself by slippage when you try to move the truck. Sometimes a bad pilot bushing may cause the transmission input shaft to continue to move making it difficult to shift.

Bottom line, it looks like it's time to look inside the bellhousing. If you have an inpection plate you can visually check from under there. But, I'd be leery of getting under that big truck unless I could lift the rear wheels to keep it from moving.