increase payload capacity 2004 Suburban 1/2 ton

How handy or motivated are you.?

If I am reading correctly, your truck has a 10 bolt rear end. Very sad.

12, or even better, 14 bolt axles are plentiful and a super easy swap. Do a spring pack at the same time with higher rate leafs.

Dana 60, 70 and 80 work too with 60s being most common. You will need do modify your driveshaft for sure either way. But an excellent time for a tranny swap as well.

BTW, a solid axle swap for the front is super common on these trucks as well.