I didn't use diodes and suffered no ill effects with my 2.4 radio, but it is a good idea to do. Kershaws overdrive pinions are just really big. They are needed on some of his kits, and can be used with the dewalt too. The only 2 speed kit I know of for the erevo and emaxx is the traxxas kit. You should check out these threads, lots of info in them.
http://monster.traxxas.com/showthrea...ghlight=dewalt
http://monster.traxxas.com/showthrea...ghlight=smoked
http://monster.traxxas.com/showthrea...t+installation