1996 GMC Sonoma Owner's Manual - Page 11

Manual Lumbar Support (Option) If you have this feature, there will be a knob on the outside of the driver and passenger bucket seats. Reclining Seatbacks (Bucket Seats or 60/40 Bench) To adjust the front seatback, lift the 1eve.r onthe outer side of the seat. Turn the knob counterclockwise to increase lumbar support and clockwise to decrease lumbar support. Release the lever to lock the seatback where you want it. Pull up on the lever and the seat will go to an upright position. 1-3