Just installed the ecu map, air filters and spark plugs in my 14' G63.....could not be happier.
Car feels like it lost 2000 lbs of weight, I think I am the only guy hunting down M5's and 991S for a drag race in my huge crazy fast G63.
So much happier than when it was stock, as the stock configuration really did not even feel like the bhp numbers MB says it is.
Car runs smoother, initial throttle is more responsive except for when you lean into it you can hear the turbos spool up and BANG the thing is lighting the wheels up, so nuts, love it.

i assume any ecu changes will take a bigger hit on fuel consumption?

Actually, I picked up 1mpg in the last 300 miles with the Weistec tune, runs much smoother on the bottom end and the crazy rich cold start is not as long in the morning, so I am really really happy.

Cort,

Where did you get that done? I don't have a distributor here in Louisiana. Will it void the warranty on the car?

I had my mechanic, friend of mine, pull the ecu, which is really simple (on top of motor, just unplugs), and we sent it straight to Weistec where they flashed it and shipped it back. Reinstalled it, fired it up, warmed it up and BANG, the thing rips....
Not sure about warranty, I know I can re flash it to stock if a real issue ensues.

Cort,

Did you need to change the spark plugs and air fliter when you did the ECU upgrade or was that just your preference?

Just my preference, but I can tell you, one thing that is really cool, is that with the new air filters you can hear the intake and turbos spool up, its really cool.

Thanks for the input on this!! Looking to do this mod as well when my truck gets here next month.