My 2005 STX 4.2L truck will start to overheat as I am traveling down the freeway. Truck has been up to operating temp for 30+ minutes and miles with AC on, then just gets hot enough to throw a coolant alert. After a few minutes it cools back down to normal and all is OK. When I exit the freeway and travel in stop and go situations it will do OK or it will get hot and return to normal. I have checked and do not have any coolant loss, no noise to indicate a fan bearing or water pump problem.
Where should I check next?

 

 

I would also say sticking t-stat, and you might as well flush the system when changing it out. I don't think its the clutch fan because it only does it on freeway. If you drive in high grass it will get caught up between the radiator and ac condenser (ask me how I know)

 

I would go ahead and remove the radiator and flush it out. My 2000 4.2 squirrel hunting rig would overheat pulling a slight grade on the highway, I replace the fan clutch, Tstat, then pulled the radiator and had it flushed and rodded out. Now it stays nice and cool.

 

check your belt tensioner and all your bearings . new belt ,replace reserve tank cap .it is your pressure cap most don't know that .
Fan clutch does not come into play at hwy speed .
sometimes the ac compressor may be starting to seize locking up cooling belt.