code p0420 on 2006 ranger with 3.0 v6 on 2006 Ford Ranger

replaced cat with bolt on walker. all 4-02 sensors. sparkplugs and wires. cleared code and it comes back after driving 25 miles.I bought code reader with live data . but not sure of readings. what should normal readings be

To understand your new scanner, purchase a Haynes techbook OBD-11 & electronic engine management systems - #10206. The code P0420 indicates Catalyst system efficiency below threshold (Bank 1). Bank # 1 converter is the side with # 1 cylinder, bank # 2 converter is the other side of the engine, and then you have the rear catalytic converter. The rear converter wasn't the issue if that is the one you replaced.
Catalytic converters have a very long life normally. So before a converter replacement, you should find and resolve the reason that the last one failed if indeed it is bad. has some very in depth scanner troubleshooting on YouTube that you might be interested in.