Go to this website... http://www.squarebirds.org/dcforum/DCForumID1/1029.html
... and scroll down until you see a post made by 63tbirdrick
That post was from me. (Different name, used to have a 63) I am having same issues as grandpaws57. The locking up is pretty bad and dangerous. I doubt its the installation if the two boxes are in different types of cars and having same problems. At first they said that the fluid temperature is getting too hot and causing the tollerances to close up and to add a cooler to the system. I did this and the problem did not go away so i added another cooler and the problem is still there but not as bad. This is basically fixing the symptom and not fixing the problem. Gearheads seems reluctant to respond to these issues for some reason. I am hoping to get this resolved soon as my summer cruzin plans went out the window in a hurry.