Hello I will help you with your question,
The towing capacity of your van is 4600 lbs.
How much does the current trailer weigh loaded/wet?
The heat dissapation of the trans cooler and the radiator will help the engine and trans stay cool but will do nothing to increase the weight capacity of the suspension.
The GVW (Gross Vehicle Weight) is not the towing capacity. The GVW is what the suspension will carry and includes the weight of the vehicle, the fluids and the cargo placed inside the vehicle.
Your towing capacity is 4600 lbs and a class 3/4 weight distributing hitch may push that to 5000 but the braking system is not rated for more than the 4600 lbs.
If you want to tow more and be safe you will need a larger capacity vehicle.