Why is my check engine light back on?

So I took my car to the shop because it cut-off on me twice while I was driving on the freeway. The steering wheel locked and the engine cut off but the radio was still on and the check engine light was on. I put the car in park turned it off and it restarted just fine. I drove maybe for 20 mins and then it cut-off again check engine light on. Again I put the car in park turned it off and it restarted just fine. Mechanic said one of my spark plug wires was melting, that's why my car cut-off and the check engine light on. He suggested this time I get high performance wires so they can withstand the heat since I've had that problem before. I did just that, I've had my car a couple days now and the check engine light is back on and my car is shaking while I drive not a lot but a suttle shaking, like a chugging shake.