Dear Radr,
I am sorry to hear you are having problems with your front diffs.

Any time a diff is shimmed, if done correctly, it should be an improvement.

First, the Photon comes out of the box with both front and rear metal diffs! If your LHS is asking you to upgrade to metal diffs (especially if they claim to already have replaced one front diff, they would have seen the gears were metal!) I would double check on their expertise regarding this types of issues.

There have been almost zero issues with the front diffs. To be honest, some people have been blowing the rear diffs (this is were most of the torque goes) and it always difficult for us to determine if it a defective part or if it is caused by user error (like banging into walls, etc.)

When developing and testing this product, a decision was made to not "hard code" the Mamba ESC so as to allow the user the full potential and flexibility of having such a great ESC!

In answer to your problem, I would thoroughly check the vehicle to ensure the diff issue is not a result of something else in the vehicle that is causing front diff problems to constantly re-occur. This is an extremely powerful car and the weakest component will always be the one to go, especially at 40+ mph. and of course, it is always possible that something else is defective or has been inadvertantly damaged.

Another alternative, If you have the optional USB cable, is to try to tone down the initial throttle surge by changing the power curve of the ESC. If you don't have the USB, you probably have no idea of what I am talking about.

I hope some or all of this has helped you.