Just bought used 2020 Durango 5.7 Hemi and having cooling issues

Took the Durango on first road trip from az to San Diego beach .. had some oil temp issues past 80 mph .. oil temp got past 255 and almost overheated… as soon as I drive a regular 75 mph it stabilized at 235- 240 degrees… I use 89 fuel and had only put a few hundred miles on it before taking on the road trip…