I got them on my 2006 Dodge truck, short bed crew cab diesel. Nothing in my instructions limited the amount of pretension like you described; 2 inches. I cranked mine all the way down for max support.
I have the Lance 855S camper as well. I loaded the camper and found that the slide side, passenger side, sagged more than the driver side, so I adjusted the driver side until the truck sat even left to right.
They definitely help with the squat. However, I found that the Hellwig Big Wig sway bar is what really made for a better ride. After putting on the sway bar, the tendency of the truck w/camper to rock left/right went away. Especially on twisty roads. Last week I drove Hwy 1 up the California coast from Bodega to Gualala and was pushing a go-fast sports car. Ha! I don't really recommend this though; my oven door opens when I corner like this and I store pots and pans in there. I found out a bungee helps with that though.
For tires, I mounted 19.5 Rickman wheels with Toyo G rated tires inflated to 90 psi rear and 70 front.
Loaded for camping, my truck weighs about 12,700 pounds with the front axle gaining 300 pounds with the camper on vs off.