I have been having an intermittent problem with my Navigator that has acted like a bad plug or coil. Under load conditions the engine starts bucking (like a bad misfire) and the check engine light goes on. The error I get during a KOER test is P1780 - Trans control switch out of range.

I guess it makes sense that if the computer doesn't know what the tranny is doing it may cause bucking. Does anyone have any idea where this sensor is and how to replace it?