Installed my 180 degree T-stat. I just ran a few errands. The last leg was about 5-6 miles in stop and go traffic the A/C was running when this was shot... here's my shots of outside temp:

And Temp gauge and yes amazingly the tank is full!

 

how the f do u get it to stay so low, my truck always overheats, i went up to the mountains few weeks ago and had to turn the ac off and slam my foot all the way to the floor to make it a few miles up the mountain. truck was redlining hot...

 

my 180 stat is perfect, stays right below the 1/2 way line wether there is a load or not, works great

 

My truck has about 73k and the tow package (so it has the heavy duty cooling). Coolant was flushed by the factory at 63k so I'm not sure what ratio they use. I put the old coolant back in except maybe a quart or two. The last part had all kinds of black bits and dirt in it. Not sure if it where it came from... could be dirt from the block, could have been in the bucket, could be be black paint chips from sliding the bucket under the truck (5 gal bucket barely fit). I made up the rest with Zerex G05 50/50. Also the radiator cap is approximately a year old. I also changed the radiator hoses out too... makes putting the new thermo in much easier. They were Gates hoses.

I also had your issue when I was going to up the white mountains to camp here in AZ. I saw them temp gauge go up about 3/4 of the way and then it went back down. I'm not sure if it was because air movement was neutral and couldn't cool (this was with the old thermo). Other than the new thermo, the coolant system is stock.