2000 TrailBlazer no heat

Blower works..Replaced the thermostat still no heat

Make sure all of the air is bled out of the radiator.
Bring the engine to operating temperature.
Both heater hoses should be very warm, (almost too hot to hold with bare hands) and approximately the same temperature, where they go into the firewall, (heater core connections).
If one hose is noticeably cooler than the other, the heater core is restricted and needs to be flushed or replaced.
Post your results.

Yes both are very hot and seem to have good flow..Im lost on this one.

There may be a problem with the blend door actuator, it has a plastic gear that likes to break. Does the vehicle have manual A/C or does it have Automatic Temperature Control?

Here is a link that explains how to get at it for inspection and replacement if necessary: http://www.automotiveforums.com/vbulletin/showthread.php?t=574779

It has Temperature Control where would I get a Blend Motor Gear for a 2000 blazer?
It does not seen to change except to defrost when i change it.If i put the floor heat on it blows from the middle.

ATC is not your "run of the mill" HVAC system. A genuine GM shop manual for your vehicle might be necessary to diagnose it. Temp not changing could be a faulty sensor, (the system has 3 or 4 of them) could be a wiring problem, a problem with the mode switch or the blend actuator. If the air distribution is incorrect, (where the air flow comes out) it could be a vacuum problem or a vacuum actuator.

If it needs the blend door actuator, most auto parts stores will either have it in stock or can order it. The Dorman part number for the ATC system is: 604-106 and it is NOT interchangeable with the manual AC system.