Ok guys, think about what your doing fitting one of these without an appropriate map. It explains why cars may 'hold' boost better, but what you are also doing is technically overdriving the turbo and sending it to an early grave, plus your fueling is not going to be right so who knows what's happening inside the block.
Basically the ECU contains a translation table of sensor reading to KPA, this is based on the voltage reading at the sensor. Say the sensor is working on a 0-5V range, this on the translation table is converting the X.XV reading to a KPA reading, this in turn determines when the ECU will add more fuel, pulse the boost solenoid to vent and open the wastegate, etc.
So by changing the MAP sensor for a larger max value sensor(2.5bar to 3bar), this changes how the readings correlate to the translated KPA reading - (i.e if at 2.75V a 2.5bar KPA sensor translates to 1.25bar, with a 3bar map sensor it's actually reading 1.5bar). So this means your ECU map will think the current boost is lower than is and therefore lower than target boost, and drive the turbo harder by not actuating the waste gate (so technically higher sustained boost), but at the same time it's only fueling for the boost it thinks it's reading (i.e. instead of 14psi, your running 16-17psi), so your engine is running much leaner and more prone to detonation, and alot worse.
But hey, you've got more sustained boost so it's good.....
As said before, get the car mapped specifically for the upgraded map sensor if you fit one..