Chevy colorado cooling issue?

I have had a hell of a time getting this truck cooling properly. I put in a new thermostat, that I know will open and close as I tested it before it went into the truck. This is what I did. Removed lower radiator hose to drain fluid. Removed the hose from the t-stat. Unbolt t-stat. Bolt new t-stat in place. Put a brand new radiator hose on. Filled truck up with dex-cool. Now here comes the problem. I left radiator cap off and started engine. Left the engine runnig for 30 minutes. T-stat never opens. The top radiator hose is hot. You can put your finger in the top of the radiator it is hot, however the bottom hose is not hot at all. And seeing as the bottom radiator hose is directly connected to the t-stat, it cant get hot enough to open, even though the temp gauge is over half way up. I have also installed a new water pump and fan clutch. Which I know work, cause if I take the t-stat out and put an empty housing in does the opposite and dosent get hot enough and the computer goes nuts. What the heck am i doing wrong here