I've been a long-time lurker, but finally registered to be able to say thank you to everyone for the great advice! Yesterday I spent a fair amount of time trying to diagnose what I thought was an issue with my filter, to no avail. I did a bunch of research on TFP this morning, and with everyone's experience here, quickly realized it was a suction-side problem. I found the issue (adjustable trim plate on bottom of the skimmer float valve had broken off, partially blocking the intake hole!) and we're back in business! In fact, it must have been partially bending into the flow before it broke because I'm now getting almost 70 GPM on max which is the highest I've ever seen.
Thanks again to everyone! And now that I'm registered, perhaps I can contribute something sometime as well.