Car overheats after driving on freeway for about a hour.

[mirage83]

Yep. What you're describing with the coolant and overflow tank is an archtypical sign of a blown head gasket. Get a block test and run it, or a compression test if you prefer.

Need to ask though, are you confident of your fan clutch? If it's bad it could explain the overheating at low speeds, though I think it may be too late for the hg even if that is what was going on.

Given the age of the car and that you've been driving it around while it was overheating, if the test is positive for a bhg I'd go ahead and look around for a reputable shop/machinist as your head and/or block may well need resurfacing before putting a new hg on.