Welcome to the forum its a great place to get your questions answered. If you are saying the bottom sections moves before the top but the unit slides out this is not unusual with rigs. Are you ensuring you are level with your stabilizers down before moving the slide? What does "GM" mean?
Jake my sidekick (yellow Lab) 10/04 - 05/20
2017 RAM 2500 CC 4X4 Cummins Diesel
2016 Flagstaff 26 FKWS
AF&AM & El Korah Shrine of Idaho