I have an 1989 S10 blazer with a 4.3l V6. It has a G80 diff in the back and it's 2wd. Ever since spring started I started noticing the temperature on my truck starts rising when I'm at a traffic block or when I'm parked. It drops when I am on the move. In the last two years I've changed the AC clutch the heater core ,the water pump and the thermostat. I also checked the radiator hoses to see if there is any leak. There are none. It's maintaining the coolant level as well. I pressed the radiator hoses to see if they are pressurized after a drive and they are hard. I also changed the oil to synthetic around a month ago. I was wondering if someone could help me diagnose this issue.