That is a connector for an ecu engine coolant temp sensor, which should be on the thermostat housing somewhere, not that familiar with your engine, but that sensor has to be on the water neck somewhere. The ecu uses it to determine if the engine needs cold start enrichment. It will probably start fine in warm weather, perhaps with a little cold stumbling, but I bet it won't start in a Tahoe winter. I bet your current mpg is pretty bad, and the exhaust smells gassy...

Not responsible for advice not taken...