Is this possibly the coolant heater motor?

Sure looks like it.

Groban's got alot of cool stuff. There's a shaft driven Howden Vane-Axial Fan 10,300 CFM Blower@ 10.0" Psi @ 34 Brake Horsepower @ 6,000 RPM. Not sure how anyone would mount it on a truck, but if it were geared up and coupled to the engine as a mechanical supercharger, the thing would sound like a jet. also a Dynamic Air Engineering 3.2 HP "Axial Flow Blower" Model No. M8862B-8B that operates on 27 Volts D.C., 117 Amps at 7000 RPM. It produces 1250 CFM @ 6.5" H-2-0.. I could see this mounted in a 5-ton air cleaner assy, but 117A is more than available. No big deal, i'm just impressed by the blowers.