okay so this is what I got 92 Ford F-350 with the 7.3idi I have an issue where the tach is interrmitt she only works when I drive her for an few hours...I've changed the sensor no change I've changed the tps sensor no change I've checked the wires don't see anything grounding out and I've checked all of my grounds and all is good...I've also tried running my scan tool and can't pull any codes I've all so check my fuses and relays and all is good...I have also changed out the vss as well as the harness and no luck...is it possiable that the tcm is ****** even though the truck is still able to start up???