It could be the version of the software you are running.
I upgraded my 1197c with the most current version and it slowed down
so bad, it wasn't useable.
I went back to a previous version and it speeded right up.
I would recommend you bring your waypoints into Humminbird PC.
Go through and see if you have any dups or if any of the coordinates look weird.
A corrupted waypoint could be the culprit.
Humminbird says that by bringing the waypoints into Humminbird PC software, it
verifies or confirms them.