Cory, when checking the pump impeller count the "veins" and be sure you get all of the impeller back. The broken off pieces if there are any are notorious for plugging "restricted" areas of flow, like the t-stat and "exit" fittings like the end of the manifold.
As this one sat for so long the "veins" may of stuck or dried out in the pump and broke off.
Where are you located? I'm also an ex multi-nut. Sailed with ORCA for a few years and even had a "C" class with a 70/30 wing sail. I got to sail on a couple of the "Bullet" series and many CSK's even Sea Smoke a couple of times. Now I am keeping my ears peeled for a ride on a big foiler.
Dave Neptune