Towing overheat today.

[Kwattro]

*Bing Bing Bing* I looked at the message center and saw "CHECK GAUGES" a quick visual revealed the temp gauge pegged to the right. Looked over at my Edge and saw 260* on the CHT. What the hell, it's like 34* outside today and I've towed in the summer before with no issues at all. Pulled over and popped the hood. No coolant loss or leaks, coolant tank full, no hiss or steam, the engine didn't even feel like it was very hot. By the time I got back in the seat the temp was 228* and dropping so off I went again. Few minutes later the same problem. Couple things I noticed. On level ground and fairly low RPM my temps would climb. Whenever on hills and the truck down shifted to 3800-4000RPM my temps would acyually drop over 20*. I managed to keep my foot into it for the remainder of the trip and had no further overheat problems. So now I'm trying to piece together why this happened. I think it's unlikely the water pump impeller would fail seeing as it's steel, so my suspects are the fan clutch or thermostat. I'm open to advice, experience, or suggestions before I begin buying parts.