Try using some dish SOP on the raider before you wash it off this will cut the road film from the raider.All so clean your air and transmission cooler that sets in front.

 

This may or may bot be your problem but it sure wont hurt. I have a 2nd gen so this may not apply the same to a later model but I think it will. You will not be able to clean the radiator very well at all with it in the truck. You just cant get to it well. A few years ago mine started running hotter than normal. Did the obvious stuff to no avail. Pulled the radiator and quite frankly was astonished at the crap that came out of it as I had hosed it off in the truck as best I could several times in the past. Some simple green and water pressure did the trick. Dont use too high a pressure as it will bend the fins. From the front you wont touch the radiator as there is too much blocking it (intercooler, ac condensor, oil cooler etc) . From the rear you have the fan and shroud.
In any case when I put mine back in no longer had a problem.

It may also be the interior of the radiator in which case if you take it out you might just want to get it boiled/cleaned at a radiator shop which would take care of both the interior and exterior.

 

My 97 needed a new fan clutch at about 60k and now my 03 with about 60k is starting to act the same way. I don't hear the fan very much til it's to about 220.

 

The CR cylinder head can get an air pocket in it, take an allen wrench and open the pipe plug behind the T-stat enough to let the air out. GW