'93 S10 Blazer overheating

Replaced my '93 S10 Blazer heater core about a week ago now it overheats everyday. It pushes the redline (260 degrees) after driving for about 15 minutes. If I stop for a red light/stop sign it cools down to about 190/200 degrees. Then it seems to be okay. I only drive between 15 to 20 minutes each way to work and thats all it gets driven daily. So when I leave my house in the morning it overheats when I get about 1/2 mile from work, but by the time I get to work the temp is okay. Same when driving home at night. Please help!!

Pretty much has to be trapped air in the system.

if thermostat is operating correctly, and there are no clogs in system, would agree about air in system. can't find it at the moment, but there is a thread here that has a fairly in depth procedure to get the air out...involves lifting truck front end, one side higher than the other and so on. point is to make the radiator the highest point in the cooling system. of course if there is a bleeder screw on the truck, use that.

here is the link http://www.automotiveforums.com/vbul...d.php?t=469926 (http://www.automotiveforums.com/vbulletin/showthread.php?t=469926)

Thanks for all the help. I'll do the air bleeding tonight.