Do I need to match the sender on my 3.0 engine to my gauge? When I run the engine, the gauge is always pegged to the highest pressure. I've got a mechanical gauge on the engine, so I know what the real pressure is

Yes, use the 911 sender. Both the 911 and 914 gauges have the same temperature range on the scale.

Did the same ,don't buy a genuine one as they are rather expensive,get one from a VDO dealer,think mine was 150C rated from memory.

Let me look, I may have a used one I can send for the shipping.