You may still have another problem. I don't think there is a "break-in" period for the OVP...it either works, or it doesn't. You are still having stalling problems, though less frequent.
The OVP may have solved a number of problems, but I still think something else is also amiss.
Keep driving and see what happens. Also, if you don't drive very frequently, you might replace the fuel filter. It is cheap, requires no diagnosis, and from some of the threads I've read, solved a few problems as well...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car