05 Limp Mode issue
 

Hello. So had a somebody changed radiator along with pipe and said I needed a 02 sensor for some reason but said yepp just do it. Got it back drove fine no more overheating issue from dash but now when I parked it started up again it went limp. When I start the car it's okay I can red line but after some seconds I can't rev past 5k . Had it towed to the guy again and he said it was just fine and he couldn't read the code for some reason. Picked it up and yes it was just fine?? Drove it around some more and started it one day. Same thing limp mode. So I didn't drive it. Showed my friend what was happening and started up fine so he didn't get to see what happens. But now it's happening once again. Seems like randomly it'll go into limp mode. What would cause this from what the local mechanic did. Could a 02 sensor cause limp mode. I remember what one was on it before and the new one he has on is way longer than the orginal.