Your PasslockII system is having a hard time reading your ignition key, you may want to have a ignition key cut for your Suburban. But make sure it's a PasslockII key, best place to have that done would be a lock smith or your local GM dealer.
Try doing a relearn to your ignition key if the key is not too worn out.
Ensure that your battery is fully charged before attempting the relearn procedure. Do not leave any battery charger or jumper cables attached to the battery. Close the hood completely. Some applications require that the doors remain closed during the procedure.
96-99 GM
1. Rotate the key to the start position to attempt to start the vehicle (the vehicle will not start).
Allow the key to return to the all position (same as if the vehicle would have started). The theft system light will flash (or stay lit) on the dash for approximately 10 minutes.
2. When the theft system telltale stops flashing (or turns oft) turn the key to the off position for 5 seconds and then attempt to start the vehicle. The vehicle should start on this cycle.
3. Once the vehicle is running, the password relearn is complete.
00 + GM
1. Rotate the key to the start position to attempt to start the vehicle (the vehicle will not start). Allow the key to return to the on position. (same as if the vehicle would have started)
2. The theft system light will flash (or stay lit) on the dash for approximately 10 minutes.
3. When the theft system telltale stops flashing (or turns off) turn the key to the off position for 5 seconds and then attempt to start the vehicle.
4. Repeat steps 1 through 3 two more times for a total of 3 cycles/30 minutes.
5. On the next cycle of turning the ignition key from off to crank the vehicle should start
6. Once the vehicle is running, the password is learned and this completes the cycle.
7. Clear any DTC's with a scan tool if necessary. DTC history will be cleared after 100 ignition cycles.
I gave you both reset just in case your Suburban is a 2000 and not a 99.
Good luck and the first one above should reset your ignition Passlock to your ignition keys.