Sounds more like a tongue weight issue to me. The coil springs in the back of my 6.0L Yukon are really soft with an anemic spring rate, and I doubt the Z71s are much better. Mine can pull well, but tongue weight kills it so I use my truck for heavy (tongue weight) trailers. I would install your airbag helpers first and go from there. If you don't have a trans temp gauge, you should get one if you plan to run it In the mountains. The weight of the trailer your running isn't that big of a deal for your suburban if you fix your spring rate issue. I definitely prefer double axle trailers vs the single ones from a stability perspective so you might like the sway control on it since it looks like a single in the pic you sent; personally, it wouldn't bother me at all with that suburban/trailer as-is if you install the airbags. However, just remember that single axle boxy trailers can get a little squirrelly on a winding road if you're not careful. Does the trailer have brakes? How are the ones in your Suburban?