I have a navigator and find it slow when there is low flow through it. This can be caused by either a restriction within the navigator itself or when my filter becomes dirty and needs back flushing. There is a single phillips screw on the bottom of the unit where you can take it apart to clean out any obstructions. There is also a three position selector on the left rear side of the unit just under the main body that controls the height it will climb up the walls. The default is position 2 but I've fooled around with mine and like 3 better (seems to effect the speed). The manual says if it climbs out of the water and sucks air then move it to position one. The manual is available on Hayward site or I can email it to you if you have trouble finding it.

Glenn in rainy Toronto