The 6.2 is a solid trouble free engine. The 6-speed transmission is great, and gears can be locked out, as needed, to avoid constant up/down shifting. Most 250s came with 3.73 gears, and about 12K towing, GCWR about 19K. If the truck has optional larger 18" wheels/taller tires, your actual gearing could be closer to 3.55.
With any gas engine, towing near wt limit, it is the gears that make the difference. That truck will work, but would work best, if it had the 4.30 gears, for the 12K loaded weight FW.
Jerry