[suicideneil]

I don't really see the point given it would be used as a direct replacement for a 'standard' in-runner ( in terms of gearing and such )- stick any typical 4 pole motor in the truck and gear it down on 5s lipo & it'll pull tree stumps all day long. There are plenty of guys hoarding 1518 & 1717 motors around here who will probably sell you one, otherwise there are various cheap options about...

Also worth mentioning that the 3906 tranny will be fried instantly with that much BL & lipo power running through it- the plastic gears are no good at all for your plan ( unless you have ~$400-600 for an uber rare set of UltraMaxxed gears which crop up occasionally on ebay )...