I have a 2003 F-350 with a 7.3L, I have had 4 pedals go out on me in the last three months. They start off working fine, 1/4 inch of movement and RPMs rise. Over the last weeks it has taken more pedal to make the RPMs go up. Over an inch. Once you put a new pedal in it it works fine for another month. When the pedal would fail it just stays at idle. It starts doing in say 1out of ten then it goes to eight out of ten. Any ideas.