Your dif cup mod looks the business! Dont really know what could be causing your engine troubles though, never had that problem with any of mine. As for the spares, definitely keep a couple of packs of cvds around, they tend to bend pretty regularly. Maybe two packs of upper and lower arms would be a good idea to keep you on the road. Other than that the cars are really quite solid, although like any car, if your gears aren't meshed correctly you will strip them so possibly order a second set of them too. Hope this was of some help.