If you do go with heavier springs, these springs are worth looking into.
https://www.tuftruck.com/products/ttc-1211-rear-suspension-coil-spring-kit/
Call the folks at Tuf Truck - they are very helpful.
As others have said, check your axle, wheel, and tire ratings if you go over the sticker weights. Brakes come into play as well. If I remember correctly, the axles are rated high enough that you have a bit of extra there.
Officially of course, you are limited to the sticker, but I'm (very successfully) using the 1211 springs, (as are many others on this forum), I pull a trailer, and will run right up to the limits, maybe a couple of hundred pounds over. Added Eiback shocks and struts (very mild lift).
Of course a new, heavy duty, truck is the best answer, but these springs are only a couple of hundred dollars.