4) check multiple data sources.Good advise. Additionally, before I raised the powder charge, I would first:
1) Crony the loads to see if they are reaching stated velocities.
2) Make sure the problem isn't from the gun.
3) Check to see that the crimp is tight enough.
Using Hodgdon's online data (http://www.hodgdonreloading.com/data/pistol), for 130gr 9mm they show 3.9gr to a maximum of 4.3gr of WW231.