I've a Polaris 380. It worked nicely last season, but now that I am getting ready for this year it is operating weakly. I checked the wheel RPM per the users manual and found it to be slow - it's about 24, but is supposed to be between 28 and 32. So, it does not have the strength to crab around the side of the pool; it just sits there until the reversing unit pulls it back and it may just retrace its path over and over. I do not have a restricting disk at the pool wall; and the pressure regulator is shut, allowing full flow through the hose.
Booster pump is new.
Backwashing the DE filter makes some difference, but with a recently backwashed filter it behaves as described above. I have not opened and serviced the filter since last year, so I'm guessing there might be some restriction in the filter. I'm planning to do the filter myself this time, after observing the pool guy do it last year.