WFCO converters have a poor reputation for bulk charging (14.4) if they even get into that phase. There are other converter brands that will significantly improve battery charging particularly when attempting to do so via generator.
I don't attempt to fully charge my batteries using our genny, rather I expect our Iota DLS converter to bring batteries back to the 80-90% range within a couple of hours as the remaining percentage could take an additional few hours.
You can connect an additional portable charger (BD 40 amp is popular choice) along with your converter to help speed things up while charging via generator, but a good start since you just added a pair of batteries is to upgrade your converter. Call Randy @ BestConverter.com for a easy upgrade to your existing system.