Took it out on the first trip of the season, after having replaced the leaf springs and tires.
It towed like a dream! As I was driving down the highway, I was thinking that it towed 100 times better, but probably really only 10 times better. It towed fine before, but was a bit bouncy. Seems better planted on the road now.
Replaced the 1750 lb. springs with 2200 lb., and replaced the Load Range C tires with LR D.
I followed TitanMike's (F150Mike

) recommendation from another thread, and kept the tires at 50 psi, although the sidewall max for max load is 65 psi. Rode good, handled well, and TPMS showed that pressures and temperature stayed good.
Stopped at the CAT scale on the way, and had a trailer axle weight of 3240 + tongue weight of 580, for a total trailer weight of 3820. GVWR is 3944.
This was loaded for camping, tools, clothes, stocked refrigerator, 3/4 tank of fresh water (20 gals.) + 6 gallons in water heater, etc.