Although I cannot say I have seen this, I would suspect a neutral safety switch causing the kickdown into nuetral. Aside from this, it you have replaced the valve body and the transmission shift points were relearned properly you may have an internal issue with the pressure plates not holding in the trans. Do you notice it being more one gear than another. For instance do you notice this happening more in the shift from 1-2 or 2-3 or 3-4 or 4-5. Does it happen on upshifts or downshifts or both. Like I said if you feel this is electrical I would go after the neutral safety switch.
Thursday, May 7th, 2009 AT 12:17 PM