The bed I used to think was the only one that is electric. That's the way our '06 Monty is configured. Otherwise Jim would be on track. But seems awhile back someone had one that wasn't electric after all. Nevertheless, assuming yours is the more common build, others here have dealt with cantankerous brakes thereon, but not me. Reckon to be not much help here, and can only speculate the brake isn't engaging, bowing to others with experience there with.
If the bed slide runs normally by grinding away slowly when extending and retracting and sounds like its motor is underneath the bed, vs. the front slides' relatively smooth, quiet, and speedy glide in or out, then it's likely electric.
Joel