1998 Acura Integra P0420 Code: Power Loss at High Speeds and Exhaust Catalyst Failure

Over the past three weeks, my 1998 Acura Integra LS has experienced sudden power loss while driving. This occurs once at higher speeds (55 mph) and three times at lower speeds (15 mph). The car doesn't shake or show warning signs—just a noticeable drop in power, followed by the engine running for a few minutes before shutting off. Restarting takes about 8 to 10 attempts; after it finally starts, the vehicle runs normally. Initially, no check engine light appeared during restarts, but now the engine light is on and the diagnostic code reads P0420—Catalyst Efficiency Below Threshold (Bank 1). There is no visible damage to the exhaust system. I'm concerned about whether a replacement catalytic converter is needed. Some online sources suggest using lacquer thinner in the gas tank to clean the catalyst, but I’m uncomfortable with that method. Others recommend physically cleaning or replacing the converter. Are there any other likely causes? Could it be a faulty gas cap or oxygen (O2) sensors? This vehicle has reached 175,000 miles and has generally performed well until now. Any advice would be greatly appreciated.