Dometic 320 has weak flush using Water Pump

I replaced my Dometic 300 all plastic toilet with the Dometic 320 without the spray wand. The old toilet flushed fine using the 12v pump. There was plenty of pressure but the seat made so much popping noise when you sat on it that it woke everyone up and the seat couldn't be replaced without a lot of modification so I bought a new toilet. After reading numerous great reviews about the Dometic 320 toilet, that's what I bought. When flushing using a city water hookup it does a fine job of cleaning the toilet bowl but when using the water pump, the flush is weak and requires further cleaning. All faucets work as they always have so the pump isn't bad. Would a new high volume water pump be the solution or is it just how the Dometic 320 is going to handle flushing with any 12v pump?