I'd suggest to look at both the load center in your RV and the load center that is powering the receptacle you plug your shore cord into. Look at the circuit breakers and make sure they are rated at 30 amps. It is rare but there were single pole breakers made in higher amperage ratings. You don't want any higher than 30 amps.
If your new shore cord is failing, I'd suggest to replace the end with a quality after-market plug. Look for something that costs more than $10 at the big-box stores or at an electrical distributor. Look at your shore cord wires and make sure they are 10 AWG or 8 AWG.