Hi, I picked up a 300cd for 350$ the other day that had been sitting for atleast 20 years. Through some diesel in the secondary filter and it fired up. Was stuck in 1st until I unplugged kickdown switch then would stay in second. No windshield! So I did not test if it shifts into third on the road. Noticed atf was overfilled so I drained and refilled it and got it to line up. Now starts in second, kickdown into 1st but then doesn't upshift from there. Any ideas?

did you change the filter?