2000 Blazer Intermittent 0300 Code with Poor Running and No OBD Codes

My 2000 Chevrolet Blazer started running poorly after a 40-mile trip—progressive stalling, hesitation, and lack of power. The vehicle would stumble or die when lightly throttled. I took it to AutoZone for diagnosis; they cleaned the MAP sensor, which improved idle significantly. However, after returning from lunch in my wife’s car, the transmission engaged roughly and I couldn’t get it out of the driveway. At AutoZone, the OBD system showed no power. Their technician suggested a faulty TPS (Throttle Position Sensor). After replacing both the TPS and the OBD power fuse, the truck ran worse. I then purchased an Actron scanner, which detected no fault codes. The only time it threw code 0300 was when I attempted to rev the engine above 1500 RPM—during that moment, it bucked violently. Despite this, the vehicle idles like a sewing machine and has no stored diagnostic trouble codes. Given that the issue appears sudden and doesn't trigger any codes, what could be causing such severe performance degradation? Possible causes include ignition coil failure, catalytic converter issues, or fuel system problems. Any insights on how to diagnose this without relying solely on OBD2 readings? Thanks for your help.