I've had this same problem on a 98 model (I believe the latches are the same). Beating it just above the keyhole (a light tapping with a closed fist) will usually work. Do not beat it too hard or the lock may get broken/bent.
If power door locks equipped, then unlock doors. If not, then use key in liftgate. Now feel around in the recess (with your hand facing you) above the license plate in the center of the liftgate. You should feel a rubbery surface slightly raised. Pull with fingertips and the liftgate should swing out and upwards. To close, pull the liftgate down and push closed. Most models will latch and relock automatically.
no liftgate release on these suburbans, the relay is on the passenger side pillar at the bottom, near the floor. and yes you will have to pull the plastic off. it is a standard 5125 relay to replace. about 5-10 bucks.
The Caravan - 1916 was released on: USA: 17 September 1916
Caravan of Camels - 1903 was released on: USA: January 1903
Just remove the plastic cover that is under the steering wheel, it has 3 screws and some snaps. then you can see the mechanism that the cable was pulling to release. it is a lever just reach in with a stiff wire with a hook on the end and hook it and pull towards you and it will release the brake.
Phantom Caravan - 1954 was released on: USA: 6 May 1954
Hollywood Victory Caravan - 1945 was released on: USA: October 1945
My hood release sticks because the post on the hood and the catch need new grease every so often. I have to have a helper pulling on the release lever, and myself lifting on the hoo to pry it out of the catch. A little grease on both parts and it works like new.
Pulling U - 2010 was released on: USA: August 2010
Pulling Strings - 2012 was released on: USA: 2 June 2012
Pulling In - 2006 TV was released on: USA: 3 September 2006
While You Were Out - 2002 Williamsburg Comfortable Caravan was released on: USA: 9 July 2004