Looking at Daves post it strikes me Dave is observing that the Rio Carp line isn't measuring up on the rod the same way as the SLX or Grand already have and I think it's pretty fair to say that of the three lines that the Carp line from Rio puts presentation first above other properties - looking at the taper on-line suggests that to me, anyway.
I have some lines like that - take too long to get used to... I use them to tie up my roses
Stick with the SLX or the Grand is my view Dave.
You can persist with the Carp line and you'll get there eventually, but as both the Grand and the SLX will present delicately with timing I know what I'd do with the Carp line
Can't say anything about your casting without having seen it first.
H