I have a problem with the TH400 in my 68 El Camino and since I don't have a clue I'm looking for ideas......With the tranny in PARK, the car will roll if on an incline. Also when the rear end is jacked up, in PARK you can turn the rear tires by hand. I have checked the shift cable, it seems OK, and the lever on the side of the tranny seems like it is as far forward as it will go for the park position. The tranny was supposedly rebuilt 3 years ago (I just bought the car in February) and has no more the a couple thousand miles since then. Fluid level is also OK. I would appreciate any ideas on what to look at next.