Do you hear a "clacking" noise when the motor is running?
While I do not have a superslide, I have had retraction problems when I over loaded the dinette. (It is my wine storage area.)
Move everything you can out of the slide as see if it will retract.
If not the gearbox might be broken.
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Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW