my grandfather has a 92 Monaco crown royal signature series diesel pusher with an Allison 3060 world transmission. It had a R-N-D keypad for shifting. After you drive for a while if you stop and put it in N the keypad begins flashing and there is no transmission engagement. If you shut it down for 15-30 minutes or so it'll be fine until the next time you stop and put it in N. Other than this issue the transmission operates correctly. Please help.