Only starts getting hot when in idle-parked/light or drive thru. Does okay when on the highway.

Fan can spin a quarter turn or more if you reach in and give it a whirl, same whether the engine is hot or cold. No grinding or anything like that.

All else I can think of is the thermostat or air blockage. Not the latter from looking, and the former seems unlikely based on my GM experiences.

triton v8, 97 model. Any ideas to save me a road-side repair day?