My '05 has a Johnson impeller pump. What's a Sherwood pump?

When you checked the impeller, did you remove it and make sure all the vanes are intact. If the engine is turned over dry it can rip the vanes off. They then block passages in the engine.

Were you taking on water. If so, you may have missed re-installing one of the intake hoses to the pump.

After that i would assume a stuck thermostat.