My floor vents and dash vents don't blow warm air anymore... where is the vacuum actuator?

 

Recently changed my heater core and when taking out the dash you have to remember to reconnect all the vacuum lines. I would suspect you forgot one.

 

Well. I flushed the radiator and put new fluid in. That helped a lot, but I think that the thermostat might need to be replaced because the engine won't heat up at all now.

 

Have you checked the intake gaskets?? Sounds more like the thermostat. I have an 01 Blazer TrailBlazer and It had a new radiator put in when the intake gaskets went the first time. They let it go so the transmission was rebuilt too, all by GM. One thing I have learned owning 2 blazers is that the original intakes are plastic and blow easily. SO when GM rebuilt it they put the same gaskets back in that the factory uses and it happened again but quick thinking saved it. Thermostat was tuck open, radiator flushed, new top of the line gaskets to be sure this doesn't happen again soon, and voila, good as new. I recommend thermostat before anything intakes would be if she were overheating.