We have a 2004 CE300 international school bus. It has a DT466 non EGR and a Allison 1K2K. The driver says the speedo is erratic. On a test drive, at first the speedo does not work then starts working but reads all different kinds of speeds it appears to work till you come to a stop then as you drive along it is inop for awhile. The transmission shifts good and codes 141 and 142 come up on the computer but go to inactive when the speedo is working. Our buses are limited to 62mph and this bus still has its limit. We have inspected the exciter ring in the trans its ok, the cluster was swapped, the speed sensor was swapped, the engine ECM was swapped, and the trans ECM was swapped, and the wiring traced and ohmed and no resolve was found. The Allison program on our computer shows no codes and all sensors working. We are having trouble finding the correct wiring harness schematics and have been consumed so deep that we are grasping at what is left of our hair. Thanks in advance for the help.