If you are running a 3 cell LiPo, you should have one FAST stock truck! It's like running a 10 cell NiMh!
Usually to be fair in stock only 2 cell LiPo packs are allowed.. Check with your track to make sure they allow it without cheating!
Bulldawg gave you a lot of good info!
Just be careful when charging.. make sure the charger you get is set on the correct profile for LiPo and amperage. You'll find them much easier to use and maintain than NiMh.
Have fun!
Jerome
