Okay. Mine is also a 3500 lb axle & spring combo. Trust me...you're not going to bottom out 3500 lb springs. I actually took a leaf out of mine to try to soften it up a tad. It's pretty much identical to yours except spring over. I did the spring over to match the Rancho lift appearance wise. Its currently on 35"s but I will upgrade to 37"s when I get some new shoes for the Hummer. I positioned the fenders to allow for mud-caked 37"s with a couple inches to spare. This seems to match the fender-to-tire gap on the truck as well. I'm not running any bumpstops...not sure what you could put in it to bottom it out (gold bricks maybe?).
I stack some serious weight on my mine...routinely. It hardly squats at all. I have had it full of sand, blocks, firewood....you name it. I run 20psi max in the tires and they absorb a lot of the bumps, (especially important when its empty). Any more tire pressure than that and it tends to bounce around on highway bumps. I should look into some lower rate springs...but I've got this set-up tuned pretty good. I just happen to be clearing some tree tops this week, and the timing on this topic is perfect. Here's some pics from this morning with a load of rotton maple tops. The third pic shows the spings with a full load...
