1998 GMC Sonoma Owner's Manual - Page 17

Manual Lumbar Support (If Equipped) Reclining Seatbacks (Bucket Seats or 60/40 Bench) To adjust the front saatback, lift the leveron the outer side of the seat. Turn the knob to the left to increase lumbar support and to the right to decrease lumbar support. Release the leverto lock the seatback where you want it. Pull up on the leverand the seat will go to an upright position. 1-3