[Saltheart]

My opinion would be that the 20 lb line is too heavy and stiff for the small diameter spool on the 5500ss. This will cause it to take a "coil set" that is it will have curvature along its length do to being wrapped around the tight radius of the spool (like a slinky). This length curvature will result in a lot of twist do to the way spinners take up line.
As far as the slack goes , every 10 casts or less if nescessary , cast out and reel it in as fast as you can. That will tghten that line back on the spool periodically. Between going to a thinner and limper line , and taking up the looseness every now and then , things should improve.