I swapped a 4L80E into my '89 V3500 using a harness and computer out of a 1991 R3500, with a 2002 4L80E. The ECM is a 16147060 PCM which controls the TBI and 4L80E. The problem I am having is that the rear output speed sensor of the trans is reading about 1/2 of the reading it should according to the service manual. I have tried swapping the front and rear speed sensors on the trans, tried rewiring and bypassing the DRAC module using the setup for a 4wd truck and it doesnt work. Im at a loss of what to do, and I would really like to get this to work properly. Only thing I can think of now is that the PROM is trying to read a reluctor wheel with 20 pulses per revolution instead of 40 which is causing it to read low.