OK this is something i know about, i tow a 1400kg trailer + gear in the cargo section (ie)12volt fridge, tools, recovery gear and so on (don't know what that is in pounds) when ever we go away, only time i don't tow a trailer is to work and back and day trips.
I use Lovell 3" lift HD springs MADE HERE (Australia), but OME HD springs are just as good and that was my previous setup (2" lift) combined with the OME shocks they work well (don't get Ranchos they break when carrying heavy loads)
You can get Polyair bags and a lighter duty springs to make it even better and an advantage with this is, you can level the truck and trailer out using the Polyair bags and when not towing let the air out to around 5psi and you can go wheeling with no restrictions, sort of best of both worlds nice soft spring for wheeling and pump up the Polyairs when towing a heavy load, speak to ARB about them both.
I think a company in the USA make a similar air bag but the name escapes me, truck spring or something like that i think there name is.
Hope this helps,
Baz.
My setup, it's a camper trailer the top opens up into a tent setup.