I think that aluminum radiator is calling your name, dude. Did you wire the fan to run all the time the engine is on, or is it thermostatically controlled? Is it kicking on? I'm still wondering what condition your radiator is in. Sounds like a freakin' mess really. Even after driving at 130mph and then going straight into city traffic, I've never had a problem since replacing the radiator & fan clutch. You'd be really surprised what a new radiator can do. Good luck. Oh, and get a high-flow thermostat (Robert Shaw makes good ones).
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Capri306, Moderator, The Mustang Works Online
1979 Mercury Capri, 5.0L -- C4 -- 2.73
1987 Mustang LX Notch