Not an Allison but hoping someone here also works on gasser trannys. Got one here that if you go from park to reverse it will not move. It goes into reverse but that's it. Move the shifter to drive and it will operate fine, goes through the gears with no issue. Go from drive to reverse and it will back up a few feet then stop, feels like park engaging. The linkage and cable seem to be working properly and everything external seems to be in place.
