I wanted to put this here for others to learn from, as I did past weekend. Ever since the T-stat debacle, I have nevr liked the way the engine cools, especially with the new radiator. It would fluctuate too much, IMO. Idling with AC on, it would get to 230ish and not come down until moving. Based on other's experiences with this, I thought this was normal and just early technology and poor cooling characteristics of GM. I tried a 195 and a 180...same behavior. Well, leaving Costco on Sunday, the truck got hot and kept getting hotter until "check gauges" light came on and it OH'd. I pull into a parking lot, the top hose is hard as a rock, no fan engagement and I am PIZZED. I immediately know the T-stat is not open. Long story short, I cool down for 30 minutes, pull the t-stat, and get it home 30 miles away. It never got above 160-170 ish on the drive home....traffic or not. I go to the parts store, get a -T-stat, regular AC Delco 195, and notice right away that it's a shorty.....much shorter than the ones I had been using. I look at the bottom if the one I pulled earlier and notice the foot is frickin bent!!! So, my assessment is this. The long t-stat was never opening all the way due to it being too long and getting obstructed. It was "kind of" working, but not to full capacity. The shorty has the room to open all the way. Since Sunday, I have driven it everywhere with the AC on, in traffic, as well as highway. It stays at 195 and the hottest it got idling in traffic was just above the 210 mark, but it immediately cools back down to 195....like it SHOULD. The fan also engages like it's supposed to. I am pretty sure, this entire time, the T-stat has been the wrong one and too long to operate correctly. I just wanted to share this for anyone in the future. It was trying to open, but it was bottoming out. I think the issue has been resolved for now. Hope this helps someone else along the way.