Suggest evaluate Converter and Battery (battery,as others suggested).
I recommend you visit You-tube video by "All about RVs" @
-Upgrade to a Smart RV Converter Charger Is It worth it?) to check and replace the converter. Mine was a YES. This is an excellent explanation regarding the battery and the multistage converter.
I changed out my converter to a smart version and it fixed the issue, plus the battery holds a charge better and should add to the life.
It took about a year and I had trouble with an inline fuse/reset button while operating the slides. As you did, I increased to 20 amp. Still had problem. Coincidentally, purchased a new battery and eventually the battery was not holding a charge sufficient to power the slides (reset required).
Best Day Ever!
David