As for the slow slide, if like my 2002 PA main living slide the engine has to be running, parking brake on, and batteries good and charged else it will need a push assist. My slide runs off the chassis battery. The it on shore power or generator so the converter is powering as well. Also ensure the slide rails are well lubricated. My main slide moves very slowly even when working correctly.
As for one slide working and another not, the large main slide requires a lot more from the batteries than the bedroom slide.
Vince and Susan
2011 Tiffin Phaeton 40QTH (Cummins ISC/Freightliner)
Flat towing a modified 2005 Jeep (Rubicon Wrangler)
Previously a 2002 Fleetwood Pace Arrow 37A and a 1995 Safari Trek 2830.