I have the GT51-TM which according to the Garmin compatibility charts I found, is the "recommended" transducer for the 1242xsv. The GT-41 is compatible though. What frequency are you selecting on the side view? The higher 455 khz will provide more detail in my experience than the 260 khz. Mounting angle is also very critical with those TM transducers. I chose the Stern Mate mounting system that negates the need to pierce the transom surface and allows easy adjustments in three dimensions. The SternMate website has detailed discussions about mounting to various hull types and is recommended reading regardless of your mounting system. I had to adjust mine several times to get it to read detail well and am very impressed with the current picture. Make sure your sonar software is the latest version, 20.00 for the 1242xsv I believe. Easy to update via an SD card. Mine is mounted to starboard and I tilt the motor up to improve the picture to port. My opinion is that mounting angle, depth, and location on the transom is key to a good result. I can get good sideview up to about 15 knots and downview to about 25-30 knots. Your transducer may have been moved slightly and that alone could be significant. Good Luck!