1996 GMC Jimmy Owner's Manual - Page 14

Power Lumbar Control(Option) If you have this control, it is located on the side of the driver's seat. Reclining Front Seatbacks To adjust the seatback, lift the lever on the outer side of the seat. Press and hold the front of the control until you have the desired lumbar support. To decrease lumbar support, press the rear of the control. 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.