I recently upgrade my Deegan Rally to Velineon and then immediately fried the stock backend. I ended up upgrading to Traxxas rear differential, I also upgraded the drive shaft to a Traxxas aluminum drive shaft. There is a bit of play in the drive shaft in the sense that it can slide back and forth about 1/4-3/8". Is this normal or did I mess something up?

A side question is should I have changed out the bearing from the factory bearing when upgrading to the rear diff?