Dodge Ram 2004, 1500, 5.7 Hemi - Overheating

Live in Imperial County CA.  110+ degree summers.
All cooling system parts, inspected, cleaned or replaced. Head Gasket and
heads replaced and one piston.  Temperature runs well while driving. Temp
Gauge at midline constantly.  While crossing border back to USA from
Mexico, long waits 1.5 hours or more or even at 45 minute waits, car over
heats, Almost reaches redline. This caused damage which is why all was
repaired. This same heating issue was occurring prior which is why damage
occurred and repairs done, i was advised that a larger radiator will not
resolve issue. Seems fan is not pulling enough air while at idle speeds of 500
rpm. I was advised to rev engine inn neutral to 1500 rpm which is normal
driving rpms to draw more air. Did so and turned on heater (another piece of
advise) I was able to draw the temp gauge needle back to centerline
whenever it creeped past centerline. Obviously I shouldn't have to so. It was
night time when I crossed. Still hotter than hades out here. Any suggestions.
Add another Fan somehow? Should fan increase rpm automatically on idle
or at high temp? AC also has difficulty cooling at noon to 5:00 pm. All
checked, serviced and repaired. Has separate fan and small radiator. Fan is
pulling air well.