Clutch Slipping

1995 Toyota 4Runner 4x4, with 168k miles. The clutch will at times fade when being pressed down like in traffic. At times when sitting at a stop light the pedal will fade completely out and the vehicle will start moving or die. I can then put my foot under the pedal, move it forward then pump it and it starts working fine again. The problem is irregular and does not happed regularly but is becoming more regular. I cannot find any leaks in the lines and the fluid is full. What is going on and how can I fix it.