We need to look into some things first of all. 

How good is the t-stat?
Is the clutch fan locking up?  (at temp, you shouldn't be able to move it at all, cold should spin freely)
What condition is the radiator?  Plugged, coolant been changed out?
Or it could be the water pump..

Need to do some checking and let us know what you've found out.



Generally, if the rig runs fine at hwy speeds, but at slower speeds, hot.  I'd look towards the fan clutch.