So I bought a Novak HV Pro 6.5 brushless system and it's in the mail to me now.  I plan to put this in my 3906 Emaxx, which is pretty much an FLM Emaxx now.  I have a couple of questions.

Do I need a new transmitter and receiver?  I never heard anything about this before but recently have noticed that my stock Traxxas radio system might have problems with the brushless system...is this true?

Also why do people lock their trannys in 2nd gear?  I was thinking of gearing the truck with a 13 tooth pinion and stock spur gear, this seems about right from what I've read on Novak's site.  Should I no longer use 1st gear with this setup?

1. you dont "need" a new transmitter, but sometimes people have problems with interference with the high electric current
try your stock rx/tx cautiously in the air first and test it alittle
maybe put the truck upsideown and then walk away from it like 50 to 100 yards and just make sure, you can never be too safe.

ive had high powered BL system with stock traxxas rx/tx with no problems

2nd q
people lock their tranny in second because the BL motor has soooo much torque that 1st gear is close to useless.
trust me, i locked my e revo conversion in second, i had absolutely no problems getting the front end in the air. or on its roof lol

so yea id get rid of 1st
unless u wana try to do a backflip on flat ground orrr grind gears? lol

also what kinda batteries you running?
if your not running lipo yet your missing out, thats the next step!

Still running Nimhs, Lipos are next.  But will have to wait until I get more $$ as I have to upgrade my chargers.

As Mentioned, the first gear just ends up breaking parts. Its not needed but when you do the 2nd speed conversion, you have less rotating mass and less that has to take the abuse of a strong brushless system.

Congrats on going brushless, you'll love it!