There are really only a couple options to rid your truck of sag.
-upgrade springs: Mostly TTC, cost $300'ish
Pros: Always ready to go, never have an air leak, easy to install
Cons: More $$, changes the ride quality of the truck permanently
-add airbags: Airlift, Firestone, cost $79
Pros: Only use when you need, easy install, cheap $$
Cons: potential for air leak
You can use Timbren SES which is about halfway between the two above cost-wise. They replace the bumpstops. SUPER easy install. But they only engage if the truck sags to the level where you've used all the travel, and then you ride on them. The ride for use was so bad I took them out and re-sold them after 1-way trip. It was just AWFUL.
I never thought I'd be an air guy, but keeping the ride quality of the truck most of the time, ease of install, price and dependability can't be beat.
Now that our truck is a tow-only I'd rather have the springs, but I hope this gives some insight from someone who went through some of it and has had the rear springs out more time than he'd like to remember.