Possibly having a cooling issue?
It seems my truck is starting to develop some sort of cooling issue and was hoping someone could point me in the right direction on it...
-First time I noticed the problem I was cruising at around 55 and noticed the coolant gauge on the dash go to the red very quickly and the "check gauge" light was on. Pulled off the road to pop the hood, coolant wasn't bubbling or hissing in the reservoir and no sign of coolant on the block or any of the lines. Closed the hood and drove home, same thing happened again and when I made it home I popped the hood to again find nothing out of the ordinary. Opened the reservoir and let it cool then cranked truck and drove for 75 miles, nothing out of the ordinary.
-Second time was a week later after seeing no issues, hooked to our dump trailer and towed it maybe 20 miles, gross weight truck/trailer was 7 tons. Upon getting to my destination I noticed the fan running which usually doesn't happen until well into the summer but the coolant temp was at "normal" on the gauge
-Third time was a day later... I got onto the interstate to head to school and got it up to around 70mph and noticed the coolant gauge was about halfway between where it normally sits and red, fan was also on. Slowed down to 50mph, fan kicked off and coolant gauge dropped to normal. Truck proceed to do this for my 25 mile trip to/from school but every time I dropped my speed back below about 60 the fan would kick off and the truck would read normal again...
Truck is a bone stock 03 6.0, any ideas would be greatly appreciated