I've really not been a believer in these, but I've had quite a few diesel professionals advise me to get one. So, I'm going to pull the trigger and order one but am thoroughly lost on which one. I've looked at S&B, aFe, K&N, plus a few others, and all make the same claims and show graphs and charts. I'm leaning toward S&B or aFe. Can anyone shed some light on 'actual' fuel economy increases, power, lower gauge readings?