P0441 Fault on 1997 Monte Carlo Z34: Evaporative Emission System Issue and Diagnosis Tips

I recently purchased a used 1997 Monte Carlo Z34 with the 3.4L DOHC engine, and I'm currently experiencing an issue with the Evaporative Control System (EVAP). The vehicle has approximately 145,000 miles and was running well when parked for one year. Since acquisition, the car now triggers a 'Service Engine Soon' warning light whenever started and driven without allowing the engine to reach normal operating temperature. Specifically, if I let the engine warm up fully before driving, no diagnostic trouble code (DTC) is set regardless of distance traveled. However, if I start the engine, drive for less than 5 miles without warming up, the P0441 code appears immediately. I've consulted a Haynes manual, which only directs users to contact a GM dealership—this seems overly vague and unhelpful. I'm unable to locate a clear system diagram for the EVAP setup on this model. I’ve already checked for vacuum leaks, disconnected hoses, and other common issues. I connected a vacuum gauge and observed 17 inches of vacuum before the first valve on the engine; when the first valve opens, there's still 17 inches of vacuum at the second valve, but only 5 inches remain after that with noticeable pulsing. The car runs smoothly and performs well under normal conditions despite the warning light. I'm seeking reliable guidance to diagnose and resolve this P044 or EVAP system issue without needing specialized tools or equipment. Any insights or troubleshooting steps would be greatly appreciated.