Can't' Keep Drives and Tabs Synced with Gauge
 

My Trim and drive gauge seems to be reading correctly but I have had the drive and trim cables adjusted 3 times over 15 hours of running. One will not go all the way down or have the same movement the other does, also the distance between them grows the longer I run the boat. Is there something my mechanic is not doing right? They seem to loosen up and go out of adjustment. Any input is welcome.