If you are somehow attached to this vehicle and wont be getting a new one for whatever reason… You could always use that fuel additive that guarantees you to pass a smog test. Since you almost passed without it… I’m sure you will pass with it.
Otherwise 1991 was a long time ago and cars n trucks have come a long way since then. Something 10-20 years newer are actually quite affordable and dare I say cheap as can be. May be time to think about an upgrade.