2005 Chevy Avalanche

try rplacin the thermostat first. another thing when the truck overheats, shut it off and feel the radiator . It should feel about teh same temp with your hand all over. If you feel cold spots, replace the radiator as it shouldn't have those....... Also if you have a "bug screen" in front of your grille remove it as it stops 15% of the air flow for cooling.