if you have two 75Ah batteries down to around 50 percent, you should be able to get them more than fully charged in 4 hours. even if you start at 40A and it tapers down to 30 after an hour our so, in two hours you would have put 70AH into the batteries. In fact a SWAG says that looking at your data you have put about 110-120AH into the battery in 4 hours. That should have got them to full charge. Or, there is enough other accy draw that is keeping the charge current low, or the meter measuring current isn't real accurate.
your WFCO is doing better than most, but a 55A PD or Iota or Powermax would have the batteries close to 90 or 95 percent in two hours. Now no big deal if you are hooked to shore power, but on a generator, another story. At least it isn't stuck at 13.6V forever which will never get the batteries charged.
I have a bank of 4 T-125's. if they are down around 50 percent, 250AH my 65A PD will get them close to 95 percent in four hours, if I also put the 45A in parallel, closer to 2 1/2 hours.
On another trailer I have a pair of T-125's with a 55A PD. even down to 50 percent, in less than 4 hours current has dropped to between 1 and 2 amps at 14.6V and the converter has dropped down to 13.6V.
