2019 3121RL.
You probably have a Progressive Dynamics
PD4575K18LS8. The model number is on a white sticker inside the circuit breaker panel door. I have a 2019 3130re. That's the converter I have. It is not lithium ready. However it does have a charge wizzard and a mode switch you can set it to boost mode and get 14.4vdc for 4 hours. Lithium prefers 14.6vdc.
I have 552Ah of lithium batteries running with this converter for the last 2 years. Works fine. You just don't get quite topped off to 13.6vdc (100% for lithium).
I added 400W solar panels (2 ×200w) and a Victron MPPT 100/30 charge controller. It is set on lithium and brings them all the way up to full charge.
We went boondocking on the OuterBanks of NC for 5 days. We ran out of water. Never ran out of power. Batteries were full by noon.
As for truck charging. The most I have seen via the 7 way cable is about 7A (using a Victron BMV-712 battery monitor).
I installed a Renogy DC-DC charger for charging going down the road or when going on a short boondocking trip and don't want to drag the generator along.
Here's the write up on that.
https://www.montanaowners.com/forums...hlight=charger