Radiator cooling fans?

I have a 97 dodge 2500 diesel truck and pull a 35 ft fifth wheel trailer. Truck runs cool till I hit grades the quickly heats up. I have changed the thermostate, but made no change in condition. Truck has air cond.condenser, and trans cooler mounted in front of radiator, and factory clutch fan. am I supposed to remove factory fan and install an electric fan to cool the radiator ?? I am told this is the best way to cool it at slow speeds

Forget the electric fans. there's no way that the electric fans can pull the air that your mechanical fan can and you didn't say that your problem is at low speeds, but high speeds under load. you're calling for more HP than your cooling system can handle.You have a fan clutch, is it good? that's the best start. Is the fan shroud in good shape?
Water Wetter is a joke. I do cooling tests on construction machinery. We tried this stuff on an eleven L diesel engine with laboratory test conditions and equipment. It got hotter. Best mix for antifreeze per our testing is 30% but watch out for cold weather.
The above assumes you have checked for blocked radiator inside and out. No bugs between the different coolers..Yes, they can build up there quickly..
Good Luck

you could attempt manually seizing the clutch on the fan

Yes this is a smart idea. it's really a problum that needs to be addressed by Dodge, but untill then replace the fan with an electric one that runs all the time the key is on.

I could chuck the factory setup and go with an aftermarket flex fan. they are a little louder but you will notice a big differance at lower speeds. A flex fan is cheaper than an electric one.

Change to electric fan or attempt WaterWetter product and be sure your trans cooler is up to the load also maybe put in a trans temp gauge or you will fry the trans.

I had the same problem I added a choose fan as a pusher fan outside rad blowing in an kept the factory set up the elec fan had a thermostat an could kick on at 180. It also made my ac temp blow cooler Killed two birds with one stone my fathers gm dulie had this set up right from the factory