The IMU we are using is the breakout board GY-521 which already includes 2k2 pull-up resistors and an onboard regulator for 3.3v as i have checked. The schematic can be found here: Arduino Playground - HomePage
If that's the correct schematics, the board has 4k7 pullups and not 2k2. Which information is correct?
If there is an onboard voltage regulator you must power it with 5V and not 3V3. Try adding another pair of 4k7 pullups (given your board really has the above schematics) to allow a more responsive bus.