It's gotta be the drag. Just turn the large spokes next to your crank forward toward the rod tip. I have the same reel and love it. Good choice!
Also, I think I can shed some light on why the drag is loosened off after the store put line on for you. When you aren't fishing and your rod and reel is just sitting there you should back the drag off all the way. As well as the spool tension knob. This will keep the braking systems in top shape.
I bet the store just did all that for you in keeping in their good practise.
Just remember to set the drag again before your first cast.
I am looking for a stainless steel 21" for a late 80's Evinrude. Right now im revving to nearly 6000rmp with WOT. Basically just waisting power and fuel hitting that number so I am wanting to try a 21 instead on the 19" pitch I have now. I am also hoping the cupping on a good stainless prop will help with the hole shot.
I'm also willing to try a 4 finger but not sure yet. Hence me wanting to know where best to go to talk to an expert.