I was playing with my torque app today and I notices that my evap pressure jumps over the place from about -600pa to -30pa. Is this normal behavior?

 

Yes.
Do you understand what the numbers mean?

 

only that the pressure in the gas tank is changing?

 

The gas tank is a sealed system, the gas is pulled out of the tank by the pump. What happens to the air pressure in that case?

The EVAP vent valve lets some air into the tank periodically.
The EVAP purge valve lets gas fumes into the combustion chamber at a variable rate. You can monitor the duty cycle of the purge valve and probably notice a correlation between it and the PSI change.

 

Awesome info thanks..