It's all your fault for not joining this forum about four years ago so you would have known all this ahead of time. :)
OTOH, your 75amper should get close to 80% SOC on four batts before tapering the amps, and many boondocker advisers say to do "50-80s" I happen to do 50-90s, but that last 10% takes an hour of gen time. Check my ugly graph for times to do a 50-90 on two batts, double the times for doing four batts instead at the same amps, then knock two hours off the four batt times by stopping at 80 instead of 90.
Also many boondockers have solar. They give the bank a shot of high amps for say an hour in the morning then go on low amps solar the rest of the day. The PM charging profile is perfect for that shot of gen time when the batts are lower since it will be in boost for that part of the SOC if you happen to be in that zone. OTOH the PD has the Charge Wizard that lets you go into boost at any zone, but only to 14.4.
My recommendation for your situation as described is to leave the 75amper as is and get a VEC1093DBD (forget that Can Tire thing--not the same at all) and use them as a team. If you have enough gen to run both you can run the 75 and the 40 at the same time for a faster charge and then at some point the VEC will be left doing it all from 40 amps on down (stop at 20a if you want to stop at 90%) That's what I do with my PM100 and the VEC. Also the VEC does the vital Equalize routine. Best of all the VEC has that amps read-out so you can tell what the amps have tapered down to and using my ugly graph, that tells you your SOC too.
For shore power converter and float you have the 75amper that still works as a converter (because you didn't fiddle with the voltage :) )
