Frend of mine had this problem come by him at dealership. 03 truck came in with intermintent downshifting and droping of overdrive. What he found was a ground strap running from the floor of cab going to engine block had cut through the insulation and was causing a grounding of the wires, this is under the drivers side of the transmission. On 4x4 you can see the strap through wheel well. Just passing on this info. This truck only had 14,000 miles.