LR isn't the problem.
IS isn't the problem. High res mode automatically turns IS off.
Focus could be an issue, but you can test that by using manual focus and magnification. Or, by stopping down.
Fundamentally though, that the camera and subject need to be really, really, really stable for hi-res to work, and there is no motion correction whatsoever. Decent tripod, everything locked down, cable release and/or time delay, completely static subject.
And even under optimal conditions, the benefits are a bit limited. You need to be dealing with very large output sizes for the increased resolution to be observable.