You cannot switch a standard 2 Bar map sensor for a 3 Bar map sensor without the right chip to suit. Voltage for both are between 0-5V, but range is totally different. So dont swap or you could get engine damage.
^^ This, the scales are completly different, it's not just a simple case of fitting another sensor.
For stage 1 the standard 2 BAR item is used, I would swap back immediately before you do some damage.
The boost you mention is likely to be a peak where it 'creeps'.
Also is it genuine Weber, don't buy the cheap electronic rubbish out there as they are inaccurate!
Martin