Could be a 5th gear start from stop situation (TSB on that), trans fluid could be low, PTU fluid may need to be drained/filled. I think the TSB applies though:
TSB 10-21-02 SLIP_NEUTRAL OUT, 5TH GEAR START FROM STOP, ELECTRONIC PRNDL ERROR
TSB 10-21-02 SLIP_NEUTRAL OUT, 5TH GEAR START FROM STOP, ELECTRONIC PRNDL ERROR.pdf