So I bought my truck in Oct of 2020, 2006 Quad Cab, 100k miles with the 4.7. I've only put 3k on it since I got it. Everything has been great on it, but something popped up this weekend driving around that has me semi concerned. I was running the AC and I was watching my needle slowly climb up, it didn't climb to high until I started going up hill. It started to climb to the half way point, to just above half way. It does seem to lower when I level out. With my normal is under half, by maybe 1/8th of an inch under. Maybe I'll try and get some pictures of it for better reference. My first thought is flush, tstat. Was curious if there is something else to look at?

Rad is full, no leaks. The temp runs normal until I use the AC or AC and going up hill. Any ideas would be appreciated.

 

At 103K miles and 15YO, I would check the radiator first. There could be enough corrosion of the radiator that it needs to be replaced.

 

I have a 07 with a 3.7V6 130k. I had noticed that as well with my temps as well, I figured they were from extra strain on the engine but, last weekend my temp gauge pegged out while driving up an hill with the A/c. Turned out my water pump impeller imploded and the thermostat was being stuck open. It may be something to look into as well.