I could be wrong, but it looks like Sedge.

Poor subsoil . On the sod you pulled up, was anchored in - aka, did roots take in. High temps - roots don't grow as much as when cooler days arrive.

In some areas even though it appears dead the sod feels anchored. Some area it’s not at all

Would my best plan of action be to power rake and clear out as much dead grass then overseed before winter?

Where are you located geographically? Are you sure the sod is dead and not just dormant? Northerly cool season lawns tend to go dormant in summer unless forced into active growth with water and fertilizer. While they may look dead, they're not and spring back to robust green life with fall rains and cooler temperatures.

I’m located in central Maryland. The summer has been pretty hot, the few weeks after we settled it was upper 90’s. It has started to cool as of recently and been in upper 70’s and lower 80’s