Well your published towing capacity of the Kia is 5000 lbs, and the weight of the trailer is somewhere near that. So my advice is to minimize the weight in the trailer and cargo in the vehicle and get the whole assembly onto the scales to understand what your actual weights are. Use a decent weight distribution hitch with sway control and get that dialed in properly.
I towed at the limit using an Infiniti QX4 and found it pretty stressful.
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