-Is there water damage in the floor so it is sagging?
-Is there something too heavy in the middle of the slide you can move out of there?
With ours (no bowing type of sag), if it won't come in up over the hump at first for some reason like stiff rubber wipers in winter or whatever, I can move the heavy sofa bed off of the slide floor onto the main floor, which takes a lot of weight off the slide, and then it comes up and in easily. Once it is in a little way and up to the "in height" and starts moving across, I can put the sofa back onto the slide floor and the slide comes in the rest of the way no problem.
I don't always have to do that, but sometimes I carry extra things there and it gets to be too much weight for the slide. If I don't move the sofa I can crank the slide in manually and get it up and over the hump and then use the electric motor after that.
To fix the sagging floor, maybe you can lay a metal bar that won't bend over the sag and use bolts to pull up the sag, but that might depend on where the sofa is and what it might look like if DW can see it.
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.