No throttle response, slides not moving

Could it be that the float height is adjusted wrong and not enough fuel is in there to be sucked up, or too much fuel which doesn't allow for a pressure differential, but just enough fuel to allow it to idle?

Easy to check. A clear piece of tube on the drain, and held up alongside the cab body. Should be just below the bowl gasket surface, maybe 3mm. You manual should say this setting info, and the correct spec for your model.
Not sure, but those floats can they be installed upside down? There should be two tabs on the flaot for adjustment. One against the needle valve, for fuel height, and the other against the arms where the float pivots, for float drop, max opening of the valve.