I have both the 2wd and 4x4 kit. Only thing I've upgraded is the driveshafts on the 4x4 so I am no help.
The Stampede's are a kick in the pants so stick with it..
EDIT: forgot to mention, I do have a Hobbywing brushless system in the 4x4 and a cheap Amazon brushless system in the 2wd.