I finally got back on the water today. The boat was unfortunately exposed to rain throughout the first three weeks of August, but I got it back to my own marina a week ago and threw the cover over it just as the next storm started.
Today, speed readings on PP were ready very high 39 MPH when real speed was 5) initially. However, things returned to normal over a period of about 10 minutes. It was still having some trouble controlling speed. I figured that having the electricals going was providing some heat to dissipate internal condensation in the dash unit, so I made sure to put the key back on after we stopped to set up our riding gear. By the time we were done, the PP was working fine.
For the time being, I'll assume that moisture was the problem and go with the "do nothing" option for repairs to the PP.
Thanks very much for your feedback, folks. You probably just saved me a four-figure repair.
Glad it worked out.
Sent from my piece of crap Galaxy SII that Sprint won't replace...