I'm not getting the expected amperage from the DCDC chargerUpdated 3 months ago

The DCDC charger will not kick in if your battery is full or very close to full. To get your charger to increase its output, ensure your auxiliary battery has been drained to at least 85 - 90%. Please remember that the closer the battery gets to being fully charged, the more the incoming amperage will begin to drop off.

Poor cabling can also interfere with incoming amps. Measure the incoming amps before and after the charger to ensure consistency. You can use a clamp meter or an in-line watt meter. We recommend measuring them just after the cranking battery and just before the input at the red Anderson plug. 
Ensure there are no fuses, relays or circuit breakers interfering with incoming amperage. This can be tested with a clamp meter or in-line wattmeter on the cabling on either side.