Whenever I get on the gas and floor the accelerator, my car will build boost until around 3.5k and then I can hear the turbo making a sputtering sound. Boost gauge still reads around 6 pounds (all stock), but I don't know how accurate it is. However it still reads at the same mark that it always did under boost, so I don't think it's a boost leak. It doesn't feel as powerful as it did before though. I checked the codes and the only one is a code 52, knock sensor, which has been there for a while and the car has not been acting up. Anyone else experienced this problem?