suspension issues with camper shell

Hav a 2003 4WD tacoma w 90,000 on it, an ARE camper shell, and a plywood built in sleeper. My suspension seems real sloppy on the highway and I think it has gotten worse over the last 6 months. Pretty sure I need new shocks, but want something with a smoother ride. Anyone have any ideas about wut I should get? Have the stock billsteins that came with the TRD package.

Any help much appreciated.

 

My 2003 x-cab 4wd started getting ass heavy last year when I added a shell, I still had the stock suspension. Kinda scary feeling in the turns and on the trails, I've since upgraded to the All Pro Expo spring kit for the rear, and Toytec coil overs in the front. Rides like a dream now. If you have the funds I highly recommend you upgrade your rear springs, even if you stay stock size, you will notice the difference.