You are telling me you put a solid continuous 73 amps into two GC2 batteries for a full hour and never exceeded 13.6 volts? Seems odd. And this is the Boondocker right?
I am thinking that 73 amps was the initial current and voltage quickly went to 14.6 and immediately dropped to 13.6 for the next reading.
Generally I cannot recommend the Boondocker for fast charging on generator as it has no timer to hold absorption voltage. Going higher in amps even makes it worse as the voltage will spike earlier in the charge cycle. You would have been better with 35 amps. PD or IOTA as said above is far better and about 60 amps is plenty with just two batteries.
Randy has lost his touch IMO :(