clearly the tuner was not successful in raising the fuel pressure, even though he fiddled with the regulator. if he had been, more pressure difference across injector = more fuel flow = less leaning out

that infers that either the fuel supply system is not up to the job, or that the fuel pressure reg. does not work in keeping the fuel pressure a fixed amount above the pressure the other side of the injector

as said, wiring should be first easy job along with fuel filter. those should be done on a car of that age anyway.