Garmin GPSMAP 741 xs Depth Problem

[CapnRon47]

I have old B&G instruments on my boat which include an interface between their proprietary FastNet and NMEA 0183. My old Garmin 545 was able to accept the NMEA output from this interface and display my instrument data (wind, speed, depth) on the screen. I recently upgraded the chartplotter to a Garmin GPSMap 741xs. It is not their latest model, but more recent than the 545 and it was on sale. It has a very nice 7" touchscreen and many network connections (Sonar, Radar, NMEA0183, NMEA2000). However the new 741 does not display my depth data, it does display the wind, speed data. It shows in its log that it recognizes a "DPT" statement, but the value of the depth does not show up in a 'Number' display page. I just tested OpenCPN ver 4.8.2 with my instruments and it does recognize and display the depth correctly.

I have asked Garmin about this issue and their only response it that they are using a newer revision of NMEA 0183 and that must be the problem. But I do not see any changes in the DPT statement across revisions.

Has anyone else experienced this issue with Garmin chartplotters ?

thanks,
Ron