Well, boat went into guardian mode! Shut off the motor, opened the hatch, oil, etc etc, looked fine. Cranked her up and off we went. Return trip from PCola to Destin, same thing happened half way, checked again, cranked her up and all was good again!
Came home and put the computer on it, reset codes and let run. Exhaust temp sensors at the risers were HOT! Shut down, pulled off the risers and turbulator gasket and it was corroding or pitting (not from water-looked like heat related). Took off the aluminum exhaust and then we looked at the brass fittings on each water rail and they were stopped up solid with some particulates and the bottom of the threads of the aluminum were almost gone (not mud or impeller parts or anything-looked like gunk and corrossion from two dissimilar metals?). I flush my boat 24/7!!! Has never been left in the water overnight! Looks like after my model or shortly thereafter, merc went back to cast exhaust manifolds and ditched the aluminum but kept the s/s risers. Soooo, I just went back to cast merc manifolds (500.00 a side). Amazing, you can now buy this as a kit for a motor and it comes with the two manifolds, all gaskets, a couple of longer hoses (did not want to spend the extra dollars for other brand exhaust-little to no gains-i'm not into 1-2mph gains). Thanks to my awesome mechanic!!!!! You da man Eric!!!!!

Anyway, IF you have aluminum exhaust manifolds on a motor of age like mine, you may want to take off that brass fitting and look in there and inspect it and the check ball valve! No cost involved-minutes to do.