Thank you for the donation.
From the symptoms described, problem is most likely caused by the valve body.
The 2-3 shift valve is tight and after sitting, it seizes and would not move to upshift. Prolonged driving would unlodged it and when that happens, shifting becomes normal until vehicle is left sitting again.
You would have to drop the oil pan to remove the valve body for servicing.
Saturday, June 20th, 2009 AT 2:19 PM