I just picked up, a pumking with 4.10 gears already installed in them for $375. I have Magnaflow exhaust, and Highflow cats installed already. I'm also JModing the valve body when I install the pumpking, My question is What kind of MPG should I get once the gears are in? Will it make a huge Difference? I have a 97 MK8 Base. Thanks for the feedback.