I had a oil leak start unexpectedly on a deuce with a REB kit. Got under there and found the speedometer drive unit had come out of the front of the transfer case. Discovered the REB kit gear had come loose and worked forward on the shaft and knocked the speedo drive right out of the transfer case. Took the top Hat off, removed 4 loose bolts, cleaned threaded holes, locktited 4 new bolts in and all set to go. Your gear may be coming loose too. As far as coming out of gear while driving, my truck has a plate bolted to the top of the transmission that has 2 notches in it, one for in and one for out on the REB shift lever. JT