04 ram heating issue

I have an 04 ram 1500 4.7 2wd my problem is that while towing my 27 ft. camper at hwy speeds 60+ mph it temp gauge shows 3/4 way to hot line. if I go under 55mph it cools to 1/2 like normal. towing around town run 1/2way on gauge. all components therm,clutch fan, hoses in good shape. changed anti freeze and added cooling additive still same. been told radiator clogged. 50,000 miles on truck. mechanic friend suggests new 3-4 core radiator. but I cant seem to find one for my truck.
anybody else have this problem?
Author: DODGERACER89