having had several problems with the topper on our full wall slide, my guess is that either the new topper was not the same size so the current spring tension is insufficient to fully retract. OR the spring was untensioned when the old topper was removed, and insufficiently tensioned when replaced. OR even possible that the spring is broken or the endcap is worn.
I've had to retension mine multiple times ... severe wind caused an endcap failure; missing washer led to endcap failure; and broken spring also occurred.
In every case, I managed to resolve the tension issue (after new endcaps and/or new spring) with the help of ladders and tools. I found vice grip style oil filter wrenches from Harbor Freight were the perfect size to grab and turn the roller to tension the spring.
My topper is a Carefree Colorado unit, and their online manual showed how many turns I needed ...
Pete and Debra, Mena AR
08 Diplomat; 17 Grand Cherokee Overland
it's too bad common sense isn't