Posting this thread for my brother-in-law. He is having trouble with his Diesel pusher with an Allison 3060 transmission (year is 93). Starts fine and engages into gear when cold. Can drive forever and transmission shifts smoothly with no problem. If he takes it out of gear it will not go back into gear until it cools off for a half hour or so. The selector will select but transmission (monitor) won't go into reverse or drive. So far he has replaced all the grounds he could find. I have seen on some other threads that it could be the ECU and some recommended a shop / person to rebuild for a reasonable price. Any guidance is appreciated. Thanks much Mark - upstate NY