I would think the slide is jamming about halfway out. It could be getting in a bind. If you free up the slide, you could move it in and out to see if it moves freely. This is easier on some units than others. Also, if you disconnect the slide, the motor should be free to turn. Some slides have stop switches that detect when the slide is fully extended or fully retracted while others use a torque gauge that tells the motor when to stop.
Fleetwood Providence 2008 40e
Ford F-350 4x4 Diesel 6.0L 2006
Honda CR-V 2006