Depth comes only from the 200khz signal even if only displaying 83khz.
I would first make sure all the sonar hardware is solidly mounted, no damage to any transducer cables, that the cable head(pins) are attached solidly to your head-unit and etc. . .
Then I would do a Restore Defaults.
Do all your testing and debugging with only the 1158 running.
What software level are you running?