Have The Shop Inspect the Engine wire harness...They last longer than the 119s but still after years can go.The Connectors snap and are brittle

With the cylinder head removed I Would replace all the rear heater hoses...Its Easier with the head removed

Check the EGR pipe frpm the Exhaust manifold to the Intake
Clean it out and or Update the pipe

A thermostat would be a Good Idea...at this time.