MPU6050 tips

Hi to everybody, I've started some months ago with Arduino because my company assigned me a interested project.

Basically, I have to command 2 ac motors (x,y plane) based on MPU6050's movement.

Of course, I've also 2 frequency converter to change the motors speed.So, that's it!!

Arduino -> MPU6050 ->Frequency converter (RS485,MOdbus RTU/TCP) -> 2 ac motors 3 phases

I've found a Jeff Rowberg library (maybe the most famous library for MPU6050). Everything go really well, but:

1) Why everytime I put in the code (I have to because the frequency converter I have works with max 9600 baud rate.) Serial.begin(9600) the FIFO goes in overflow?

aworld  7   0   -594
ypr 0.68    0.20    -2.43
aworld  7   1   -589
ypr 0.68    0.20    -2.43
aworld  5   1   -586
FIFO overflow!
ypr 0.69    0.20    -2.43
aworld  1   -5  -590
ypr 0.69    0.20    -2.43
aworld  1   -7  -585
ypr 0.69    0.20    -2.43
aworld  0   -4  -582
ypr 0.69    0.20    -2.43
aworld  -3  -3  -584
ypr 0.69    0.20    -2.43
aworld  -4  -5  -591
ypr 0.69    0.20    -2.43
aworld  -1  -7  -598
ypr 0.68    0.20    -2.43
aworld  0   -5  -592
ypr 0.68    0.20    -2.43
aworld  0   -4  -590
FIFO overflow!
ypr 0.68    0.20    -2.43
aworld  -4  -3  -574
ypr 0.68    0.20    -2.43
aworld  -1  -5  -576
ypr 0.68    0.20    -2.43
aworld  -3  -6  -582
ypr 0.69    0.19    -2.43
aworld  -2  -4  -582
ypr 0.69    0.20    -2.43

If You know, could You tell me what I've to change in Jeff Rowberg's code to solve this problem?

2) Although, I did the calibration and I set the offset, "z axis" acceleration is very far from 16000 (1g). What could be the problem?

3)Also "x axis" and "y axis" acceleration take long to be under "50", in fact for 15-20 seconds they are more or less 350 each. Do you know some similar module (GY-512) more stable and efficient?

Sorry if I bother You with this long question... Every tip is welcome. M.