I did airbags on the rear of mine and am going to put custom coils under the front to give me 2" of lift and 1500 more pounds. As Tommy said, Firestones from SD Truck Springs and mine have been good to me so far. Check them about once a month.
On my other truck I think the springs are sagging from age so think I'll try some Timbrens on it. I have never used Timbrens but personally I would not go with anything other than Timbrens when it comes to the rubber helpers, heard to much good about them on here to use anything else.