Big hills

All trucks produce more heat when you work them hard. At highway speeds there is usually enough air flowing over the rad to keep things under control. As you climb bigger and longer hills there is less natural air flowing over the rad so your engine fan has to kick in to make up the difference. Given a tough enough climb and the right outside temps, it may not be able to keep up.
Personally if I'm about to do a big climb I turn on the engine fan manually (some trucks don't have a switch for this) and leave it on for the whole climb, saves wear and tear on the fan clutch and helps keep the temps steady. Also I climb in a gear that still allows me to accelerate, then back it off a little, then you're not at full max power and heat, plus you have some options if you catch up to a slower truck.

 

Is your fan coming on once the coolant hits 210 or so?

You can reduce heat gain on long climbs by running at the right RPM's, etc, but if the truck is working properly you should never see an overheat condition this time of year, even if you do everything wrong.

Either the fan is not coming on, or the radiator needs cored are my guesses.

 

Overheating is not the problem. It is the part where he said:

"COOLANT SPRAYS EVERYWHERE "

 

I might be wrong. However, I think something is wrong. It needs fixing ASAP or sooner!

 

It's dropping ballast to help make it up the hill.

 

That poor, poor truck

 

Did you get the coolant leak fixed? A mechanic needs to pressurize the system to find the leak. Could be as simple as a worn or broken radiator cap, but you need to have it checked out...the truck should not be spraying coolant everywhere.

 

Since your shop checked it out, you do need to gear it down. What is your temp gauge showing? If engine is going over 210 by much, time to downshift...watch the temp gauge.

 

That pretty much sums it up