Janezki
I exploded my 3 speed last week too. (I had about 6 lipo packs on it) I also have a Kershaw Design direct drive on order. I'm also going to work on using a Ofna diff out of there dirt oval car (solid spool drive) with the motor driving that, like a truggy setup.
For answers on the Cen Gen diff mod follow this link
http://www.rcbasher.com/savcendiffs.html
I used the four pinion setup with 7000 oil in front and 5000 in the rear diffs.
I need more time to tell if these are the right weight.
I'm running a Neu 1515 1y on 4s 8400 lipo, with MMMv2 and 16 tooth pinion and stock spur/slipper full tight. That was good for 49 mph before the rear end change. The Cen Gen rear end will give you higher top end. Iplan on switching to Flight Power 6s 5000 lipo at some point this up coming summer.
Lights look really cool on your truck, how do you keep your truck body so nice looking, mine is trashed......