Your 1998 4.3L has Central Sequential Fuel Injection, (CSFI). The TSB retro-fit changes the system to Central Multiport Fuel Injection, (CMFI) which was used from 1991 to 1995 and is less fuel efficient. Before making the change, you might want to diagnose the problem with your current system. It will most likely be far less expensive to repair your CSFI.
Start by checking fuel pressure and leakdown. Key on, engine off, fuel pump running: Fuel pressure must be 60psi to 66psi and must remain above 55psi for 3 to 5 minutes after the pump shuts off.