01 escape v6

I'm having a problem with the A/C and possibly the cooling system? The A/C blows cold in town driving, but at highway speeds blows hot. Also maybe unrelated the low coolant light is also on, but the resevoir is full. I have checked the Freon level it says "normal" on a cheap walmart gauge.
2001 Ford Escape V6 XLT, around 140,000 miles, mostly highway.