Going above 55 and sometimes when going yup hill at lower speeds. I'm pushing a 91 EX 5 SPD manual. It's strange ebcause it doesn't always happen. I notice it sometimes going to work, and coming home through a hilly area. If I take it out of gear the vibration stops immediately, same thing if I let up off the gas, vibration stops. If I'm going up hill the same thing will happen at a lower speed. One morning I couldn't shift past 2nd gear going up a hill or it would start vibrating. I was told it might be the clutch, any suggestions?