I went through this last year with my car. In 80° heat it would creep up past 220° on the highway and wouldnt come back down.
Somethings to consider.
1. How is the flow on your radiator? You might want to have it rodded out since the cores can become blocked
2. How is your fan? Does the high speed circuit work?
3. Do you have underdrive pullies? The smaller pullies can cause the water pump to spin slower
4. Are the baffles still in place in front of the radiator?
I had my radiator recored. I removed the underdriven crank pulley and installed the stocker. I also replaced the stock fan with dual Spal's. Lastly, I made new baffles for the radiator along with adding ATR's side baffle kit. This past week we had temps in the mid 90's here in New Jersey. The hottest it got was 192°.
I am planning to add a B&M stacked plate racing oil cooler to replace the factory engine oil cooler (which IMHO is about worthless). I run a 160° thermostat and I'm convinced that I can get the temps down into the 170-180° range on a 100° day. There is no reason why you cant get the temps down, it just might take a little work.