OK, I found the problem. I had read that the the pos & neg battery pins on the 7 pin connector on my truck were 10 ga wire but they were not. The - wire was heavy, possibly 10 ga but the + wire was a thin 14 ga or smaller.
I ran a 10 ga (6mm2) wire from the battery, fused @ 30 amp, to the rear of the vehicle and ran 10 ga wire along the trailer cable to the input on the Victron. I ran the + wire from the 7 pin to to the H terminal on the remote on/off on the Victron so the charger will turn off when the engine is off. I used 10 ga wire instead of heavier because I had 2 20 ft extension cables with connectors from a Renorgy portable solar panel I had purchased. I never used the extension cables anyway. I ran only a + wire since the - wire on the 7 pin is 10 ga and the hitch & safety chains provide additional grounding.
The results? I now get 13.9v charge out of the Victron and my 2 LiFePo4 batteries charge at 146w @ 11a for the battery closest to the charger and 82w @ 6a for the 2nd one. Can I then assume that the total charge rate is 228w @ 17amps? If so that is good enough for me since our fridge is propane/ac.
Thanks for the help offered by this forum. I see now that I should have checked the wiring at the 7 pin earlier as chrigu and Owen suggested.