Do you have a slide topper awning? If so, that might lessen the likelihood of what I'm suggesting. But it may be that deterioration of either the coach or the slide seal across the top of the slide, on the outside, may have deteriorated to the point of presenting a tacky surface to the mating seal surface. I don't know if that can happen, or not, but it wouldn't take a lot for it to hang up the top of the slide, as the pushing and pulling likely happens at the bottom. Its something you might check, after you get the slide out.
Jim & Angie, Boise, ID
2006 Monaco Dynasty Countess III
2017 GMC Acadia Denali