Perhaps a bit of explanation is due. The vacuum cut-out switch is there to prevent runaway (uncontrollable revving) in neutral. As suggested, it does this by sensing manifold vacuum and cutting out one cylinder if runaway is detected. The problem is, in some situations, there could be high enough vacuum to cause it to operate at higher throttle settings, like at cruise throttle setting. To prevent that, the vacuum cutout switch is mounted on plastic (not grounded). The safety switch acts as the ground for the vacuum cut-out switch. At low throttle settings, the safety switch is closed, the vacuum cut-out is functional, and ready to react to runaway, should it occur. At higher throttle settings, the safety switch opens, which disables the vacuum cut-out switch, preventing unwanted operation.
All this to say that if everything is connected and adjusted properly, all this is out of the picture and isn't doing anything at high throttle settings. In other words, it is not causing your cutting out at high speed.
So, look for something else.