I tested the old thermostat and it opened fine, but replaced it anyway. I have no overheating issues now. Exactly the opposite.

 

I haven't had any issues with overheating lately. However my temperature gauge never really gets about 160 - 165 degrees while driving. I decided to check my coolant again on Friday, and as expected it was still a greenish brown color. So on Saturday I drained it, removed the thermostat, filled it with water and prestone flush and drove it all day and then drained it out again. I repeated this yesterday morning and checked it this morning, it is now mostly clear. So I will drive it for a couple more days and fill it with 50/50 water and coolant. I also picked up an AC Delco thermostat. While I had the engine drained I decided to replace the temp sensor since they are fairly cheap. I will post pictures in my build thread.