I have an
L5740 and use the diff lock quite frequently in the woods. Throttle position should have no effect on its operation, since it's just a mechanical linkage. I engage it mostly when I'm moving, as long as the tires aren't already spinning. On rare occasion I think I have taken enough weight off the seat sensor, which will cause the engine to stall. This is likely your issue if you're on the lighter side. I'm not sure if turning the seat spring down (less tension) would help or not. You could try zip tying the seat sensor switch so it won't disengage and see if that solves your issue. I had to do this running a pto powered backhoe, since I couldn't get out of the seat with the pto engaged.