The 3906 has a rep for being easy to roll over when turning. When I got a used one, it was hard to drive cause it was so easy to roll. I went on eBay and got 3.3 bulks, knuckles, tbs, upper and lower a-arms and drive axles. These are direct swap outs, but it needs to be done all at once cause the a-arms are longer and the axles won't fit the stock knucks either. Sounds like a lot, but seems the 3.3nitro stuff sells cheaper than the stuff for the 16.8 Emaxx and its the same. I did upgrade to 16.8 diffs since the ones on mine were prety shot and were both clicking when I got it.

Its drives like a diff truck now, much less tendency to roll over with the wider suspension. 3906 can still be a lot of fun with some upgrading.