Didn't think to suggest this, but Otto is correct. The TOD is remarkably sensitive and all four tires need to be the same size (all new or all with the same wear) and all at the same air pressure. The TOD works by sensing when one, or more, wheels is turning faster or slower than the others so if one tire is a different size the TOD will sense that it is spinning at a different rate than the others and engage the transfer case to push power to the front wheels.
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