ajw is asking good questions (as always it seems).
How is the flow to the rest of the Polaris? (Debris tube, tail whip, etc)
Assuming a functioning booster pump, check the restrictor plate. Also, while unit is on, raise each hose swivel above the water and check for drips or sprays, they may be leaking. I haven't installed a single Polaris unit in the last couple of years that didn't have at least one defective swivel.
Third thing to check would be the thumb screw leading to the tail whip of the unit. If that is letting through too much water, if can impact the water flow elsewhere.
Last thing would be to check under the body housing to see if any of the water management system has become disconnected or is leaking.
Other than that, there may be a blockage in the management system, though I wouldn't expect it with a brand new unit.