Have you thought of looking at a Roadmaster.
My truck, 2012 FX2 Supercrew, 3.55 gears, payload 1477
Trailer is an 23 foot toy hauler unloaded at 6,400. Loaded it is between 7,200 to 9,000 depending on the trips we take.
I have Bilstein shocks and the Roadmaster and the truck towes great. When I am loaded I am about as level as you can get with a trailer.
90% of my towing is into the Sierras and it handles great in the mountains.
Would not trade this set up for towing anything under 10,000 pounds
I think the Roadmaster is the best thing to ever hit leaf spring suspension when you want to toy or hauler a lot.
Trucks guy second, Mountain biker first