Temp gauge high after rplc radiator

[dhtrack9]

I have a gmc sierra 2000 w/5.3 engine, I just replaced my old radiator that had 199K miles, the old radiator was cracked and leaking so I replaced it. after I replaced it with a new one my temp gauge starting rising past the normal range after running the engine for 20 minutes or more. I felt the top radiator hose and it was hot, noticed when I turned on the heater only cool air was blowing (strange)......I did not change my thermostat yet and I did not replace my rad cap when I change the radiator....I'm stumped as to what could be causing this.....before I only had a leaking radiator and temp gauge was normal until I ran low on fluid.....Help please!