Problem solved. Turns out the problem was with the jet that hits the drive turbine. I finally called customer service at Polaris and described how the drive jet was not entirely hitting the turbine directly, but was spraying a very wide pattern. Based on this alone he was quite certain that there was still debris in the nozzle. Took it apart again and sure enough there was a very small stone chip wedged inside the nozzle, not blocking it entirely but disrupting the jet causing it to "spray" rather than "stream". Put it back together and it works like a charm.

The rock chip was either missed at the pool store when they did the clean and rebuild or was still within the hose system or body of the cleaner. Of course, in hindsight, the problem must of started back early in the summer when I think I ran a day or two without the protective screen in place.

FWIW: for others that have similar problem (picks up well but moves slowly) at in this case the solution was poor water flow to the little drive turbine inside. This is an easy fix if you aren't reluctant to take apart the polaris. For the 380 anyways there is one screw to remove the blue covers and one or two to remove the inner guard over the drive gears. You can then actually run the unit and view the drive jet spraying against the little turbine wheel that in turn drives step-up gears that then drive the wheels. If the jet looks like a solid stream similar to what you see from the other jets in the "throat" of the pick-up area, then it should be okay. If it is a small stream, no stream, or spraying a wide-pattern stream, then you have a blockage somewhere. You can then use a paper clip or similar to try to unclog the jets, and maybe then blow it out with compressed air or just water from a hose. Might be best to remove the 3 screws that hold the "feed pipe" in place and remove that so you can see if you knock something out of the jet. Put it back together and give it a try. If you don't find any debris, then my thoughts here aren't going to help. In that case, don't be afraid to call polaris customer service; they were helpful and friendly.