Before you start taking stuff apart- - - - -block the clutch pedal down with a piece of 2 X 4 between the seat frame and the pedal, crawl under the truck with a water hose, and flood the bellhousing with a stream of high pressure water with the engine running. A pressure washer would be even better, if you have one available. There's nothing about the clutch system that will be harmed by a high-pressure flush, and you just might dislodge all the junk without having to disassemble anything. If it doesn't work, at least you'll have a very clean clutch assembly to work with when you replace it.
Jerry
