Here's the easy/simple/correct instructions for programming/re-programming an Isuzu OEM remote/key fob:

PROGRAMMING INSTRUCTIONS
VEHICROSS: 99-01
Remote added or replaced:

1. ACCESS THE PROGRAMMING BUTTON ON THE REMOTE ALARM CENTRAL LOCKING CONTROL MODULE LOCATED ABOVE THE LEFT KICK PANEL – GREEN BUTTON
2. TURN IGNTION TO ON
3. PUSH AND HOLD THE PROGRAMMING BUTTON FOR 2 SECONDS
4. THE SYSTEM WARNING LAMP WILL ILLUMINATE FOR 5 SECONDS
5. WHILE THE SYSTEM WARNING LAMP IS LIT UP:
- PRESS AND HOLD THE REMOTE LOCK & UNLOCK BUTTON
6. THE WARNING LAMP WILL EXTINGUISH
7. AN ACOUSTIC SOUND IS EMITTED ONCE & THE PARKING LAMPS WILL FLASH ONCE
8. TURN IGNITION SWITCH TO OFF
9. Confirm successful programming by locking and unlocking vehicle.
10. Repeat above procedure to program remaining remotes.