When driving home on El Camino Real (San Francisco peninsula) I actually find my DD '04 GT slow away from a light compared to anything with a V6+ and automatic unless I really wind it up!
I know that those stock gears are the reason!
With 4.10 or 3.73 I believe that problem will be solved and even have better overall driveability in day to day traffic (I have a 5-speed).

But will that void my extended warranty?

Please advise.

Thanks.

 

If you are concerned about your warranty, you should never mod the car. Technically, the dealership has to prove that the mod lead to a failure, but they can be pretty creative.

However, what are the chances of them knowing you swapped gears? It is not as if you can see them. Be sure to keep the stock pumpkin cover and never admit it. I don't think they will notice. If they wanted to, they could easily sprin the rear and count the shaft rotations, but ar ethey that smart?