increase payload capacity 2004 Suburban 1/2 ton

If you want some peace of mind then there's only three things you can do; upgrade to a capable vehicle, reduce and get closer to your limits, or take 2 vehicles. And I'm not one of these people who will recommend getting a 1 ton for your popup. I'm one of the push the limits type people, but I know when enough's enough. What you have to remember is that there's a weak link somewhere in that truck. That's how the GVWR gets made up by the manufacturer. Which component is it? Unless you work for the manufacturer and was on the design team, then you'll never know which one. You can spend thousands of dollars on coolers, brakes, suspension upgrades, gears, engine mods, and any number of other bolt ons and never address the truck's weakest link. Could be the linkage in the drivetrain, the actual gears in the tranny, or the crankshaft.

Exceeding the GVWR to get to the axle rating is bad, but it's not really that bad of a thing. It's something that lots of people get away with. But exceeding the axle rating is in a totally different ballpark. For me that's a hard line that you don't want to cross. One thing you have to remember is that the brakes on your vehicle are designed to stop that axle's rating according to FMVSS. Also, those bearings in that axles are carrying vehicle's weight. When you exceed the axle rating those bearings have to take on more weight than they were designed to.

At your current level it's probably not all doom and gloom (I'd keep a very close eye on that rear end and suspension). You're not exceeding your ratings by a lot this time, but who knows next time. Next time you might bring a couple extra chairs, a little more water, or more food. Your kids are only going to grow, get heavier, start to bring more stuff. If I were you I would not toss any money into this truck trying to make this truck better because you won't succeed. There's been too many who've come before you that's tried the same thing and came up with the same results. I just don't want to see you stranded on the side of the road with your wife and kids and facing expensive repairs all because something broke when you hit a simple dip in the road.