Here's my situation. I was towing my 38ft fifth wheel to the Oregon coast. My clutch gave out on me twice. The first time was trying to down shift in Portland traffic and the clutch pedal was hard and I could not press it. Finally got it back in gear and proceded on my way. The next time this happened I was pulling a big long grade and went to down shift for traffic when no clutch again. I kept pushing the pedal and it was hard as a rock. Kind of like a vapor lock. I finally managed to get it back into 5th gear and a lower speed. Went this way for about 10 miles when I came to a stop light, I was in a bad spot. I kept pushing the pedal when all of a sudden the pedal was back and I could shift again. I have been driving fine for the last day. Does anyone have any suggestions on what this could be. . I have about 70,000 on the stock clutch and G56. Thanks for any help.