Recently been flying 757 200, with sim throttles I cannot get them to match, one of them moves somewhere else all the time, either one will always be different.  I have external throttles and they are matched through FSUIPC.  How can I get the screen ones to match as even with autothrottle they are different and the only way I can get them to equalise is using the mouse but then seconds or minutes later one of them moves.  I cannot see anything in setup.

When I select auto throttle as per the checklist my throttles do not match on screen, one or either will go into the red zone, I am fighting all the time with my mouse to get them to align. I also have external throttles and through FSUIPC have got the same figures for each throttle.  Any help please?  Thanks Laurie