As noted, there isn't any way to know.
However, I don't think the motor would be the issue. The frame that encloses the slide is. Generally speaking the more common issues with slides is adjustment and broken frames. That being said, I would avoid putting heavy items in any but the most secure reinforced compartments. You can always put very heavy items in the back floorboard or underneath most back seats assuming your truck has one.
Fwiw, my guess is that the motor is very similar to what they used on their jacks. Those can lift over 1000 lbs, so practically speaking you'll never run out of capacity to move the slide in/out.
'10 Ford F-450, 6.4, 4.30, 4x4, 14,500 GVWR, '06 Host Rainer 950 DS, Torklift Talon tiedowns, Glow Steps, and Fastguns. Bilstein 4600s, Firestone Bags, Toyo M655 Gs, Curt front hitch, Energy Suspension bump stops.
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