P0173 Fault on 2001 Mitsubishi Montero with CA Emissions: Diagnosis and TSB TT-150-13-001

I've been consistently encountering the P0173 diagnostic trouble code on my 2001 Mitsubishi Montero, which is registered under California emissions standards. Despite multiple repairs over the years, including replacement of the Mass Air Flow (MAF) sensor, both upstream oxygen sensors, full intake manifold sealing (including o-rings, hoses, and gasket), and upgrading to iridium spark plugs with new spark plug wires — the vehicle still returns the P0173 code. The issue persists even after resetting the code; it reappears within 10–20 miles of driving. The car currently has 127,000 miles and continues to perform poorly compared to when it was new. As a result, I’ve considered temporarily covering the check engine light with electrical tape as a workaround. However, I’m seeking reliable technical advice on how to resolve this persistent issue. Could there be an underlying fuel system problem, such as a faulty fuel regulator? A known Technical Service Bulletin (TSB) titled TT-150-13-001 specifically addresses fuel regulator-related P0173 occurrences in the 2001 Mitsubishi Montero. I’d like to confirm whether this TSB applies and if my dealer can provide a copy for inspection or repair.