Just a thought.
On my'04 Pace Arrow, I have to be in "park", emergency brake on, and engine running to put the slides in or out.
Have you tried that ?
Mike in Colorado
2004 Fleetwood Pace Arrow 37c,(Jezebel) Ultra RV ECM / TCM, PPE deep TX pan, Bilstein's, Sailun's & Sumo's all round, pushed by a 2014 Chrysler T&C, on a Master Tow Dolly.