If I was a betting man I would bet on your fan clutch-when you start your car cold build your RPMs gradually to 2000 RPM and listen for the fan "roar"-I bet your clutch fluid has leaked out. I just refilled mine with the Toyota 6000 CST silicone oil ($16 from your local Toyota dealer) and it made a huge difference with just one tiny bottle. If your radiator was plugged I think you would see high temps at extended hiway speeds(and not just uphill).

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1982 300DT 190K (Diesel Purge + synthetic oil=smoothness at last!!!)
2004 Ford E-350 6.0 L PSD 227K
2006 Dodge Ram 3500 SRW HO Cummins 4X4 48RE 42K (brute force tow vehicle)
2005 Scion xB wife's rolling pop can
1993 GMC Sierra C3500 6.2 142K