I have the GT5 and am using it in our Axial Ryft with all Tekin electronics, including their high torque servo. It doesn't get much more high end than that, and it works just fine. As far as range, I have never had a range issue with mine. I used it on a huge RC track and that was as far away...
I would maybe pull it apart and check the soldering of the antenna wire inside. It may just be a cold solder connection. Speaking of soldering... I have a backlog of that I need to get busy on... ugg 😖