Quad X frame pitch angle is always tilted forward

Hello everyone,
I have a quad X frame with NAVIO2 that runs a px4 flight stack. I am trying to fly the drone but upon takeoff it always tries to flip because back 2 motors spin significantly faster than the front 2. At first I thought it was the uncalibrated ESC problem so kept on trying to calibrate them through the Navio2. After many tries i am confident to say that this is not an ESC problem, then I thought that it might be an uncalibrated sensor or RC stick problem. I have re-calibrated the sensors a dozen of time but still no luck. I checked the log files and it shows that the pitch angle is off and that the drone is always trying to forward. Even while adjusting the pitch RC stick upon takeoff, just so all of the motors spin at around similar RPM, the back two motors still spin way faster.
Has anyone encountered this kind of problem?
Here is an example flight log which could probably shine some light on my issue.

Any advice on how to solve this is greatly appreciated. Have not been able to fly this drone since i bought it.