OK so I have a 700R4 in my new woods truck (88 wrangler TPI350/700R4/Atlas II/14ff/D60) with a TCI manual valvebody. I finally got a driveshaft from High Angle last week so I can get power to the wheels. I put the shaft in and lifted the truck off the ground to go through the gears. First is fine, 2nd is fine, but it locks up for a split second when I shift to 3rd. After that split second, everything is fine, and it goes into 4th fine. It does it while driving but its not as noticeable as it is on the lift. What could be causing this?