We have two of these units on our charter
boat. They are an excellent choice.
I assume the intake pipework is the correct size, 3/4" to 1" (19mm to 25mm). They pump more water
than a Jabsco
Seeing that your toilet is new, I would be looking at the intake pipework or skin fittings & valves for restrictions or kinks. Failing that I would check the water intake pump impeller. These toilets usually pump lots of water!
Another issue may be voltage drop not supplying a full 12 volts to the pump. They also suck a few amps, 20 to 25 while running if my memory serves me correctly.