Temp gauge reads past normal

I own a 2004 dodge ram 1500 slt automatic, its has about 70k on it. The problem I have is when I drive on the highway at 70 mph after about 15 min or so the temp gauge starts reading past normal. I cant put on the a/c while driving it causes the gauage to go into the red and set off the check engine light. I have replaced the belt, the thermostat, flushed the system the fan clucth was checked. I dont know what else to look for. There is a slight whining noise that I have when the engine is running it started when I degreased the front of the motor, due to grease and our great lovebug population. When im not on the highway the guage usually reads at normal or just slighty past, please help! It is a 4.7 l motor, the fluids were changed and or checked