my first few questions are:
what shape is the rad in?
what size fan?
What brand fan?
Stock or high flow water pump?
is the gauge accurate?
There is a good chance your rad is half toast, fix that first. Take it to a rad shop and have them rod out the core. You may even need a new core - your rad shop can help here.
Next, make sure you have air flow. Radiators require air flow, the more the better. They actually need more as much air at low speeds as they do at constant highway speeds because your engine is generating more heat under acceleration and getting the truck moving than it does at highway speeds. I would switch to an engine driven fan with a good fan shroud if you do any towing, however if you really have to have an electric fan, use a 16" fan from either Spal or Tri-Pac as these are the only electric fans that I have ever tested that actually move enough air thru a radiator. They are a bit more pricey, however they work. The Spal and Tri-Pac fans are rated at 2900 CFM with 0" of restriction, and drop to about 2200 CFM at 1.4" of restriction for the common rad core. The low dollar Hayden fans do not move enough air thru the restriction of the radiator core (about 900-1000 CFM at best). you will have to make sure you have straight fins on the rad as well. Damaged fins prevent air flow. Towing you will need 2400 - 2800 CFM thru the radiator, so you will need to start with about 3200-3500 CFM which you can only get with an engine driven fan.
Is your water pump stock, if so, you may need to switch that out to a high flow unit if you have a really radical cam with lots of advance. You will need more flow.
Red Line Water Wetter along with other coolant adatives do not work (I ran the tests in the dyno lab myself to prove it).
Dropping the pressure cap from 13psi to 7psi only lowered the boiling point of the coolant (and when your radiator boils over). Hot coolant is better than steam for cooling. I would recommend going back to the 13psi cap
Hope this helps
Scott
