Servo "relaxes" after 10 seconds and does not hold load

I am currently using the DS5160 ( servo on a large rover. The servo is approximately under 13kg of load so it should be plenty big. However when I turn the servo using my hand controller all the way right or left, after about 20 seconds of holding the load it “relaxes” back to the neutral position or close to neutral like it can’t hold the load. But if you move the hand controller stick a little it jumps back to the position. Moving the servo around it pulls the load fine and easily.

I have already checked and it is constantly receiving good power at 7.5v from the power supply. Any ideas on how to fix the servo from not relaxing but being able to hold the servo load? Is this a setting in Ardupilot? I’ve seen review videos on youtube with this servo and the 35kg one holding waterbottles just fine.