i have a 1996 chevy suburban v8 diesel and i already change the head gasket , water pump , thermostat , viscous fan , and belt. the temp is normal when running but when there is traffic my tem goes above 1/2 and the a/c starts getting warm , well im in a hot country . need help , and i think the stock water pump pully in big so that when its idle there is not enough air passing through the rad. . need some advice.. thanks

 

I know you say you changed thethermostat, but it sounds like you might still have a thermostat problem. I would check the thermostat just be sure.
http://www.autozone.com/az/cds/en_us...rInfoPages.htm

 

You might also remove your water pump and check the impeller to see if it is still moving water. Impeller blades can deteriorate over time until there is not enough of them left to be fully functional. This will result in the conditions you describe.