A few of the best upgrades to a slash that can be done to make it even more bullet proof are:
-STRC hardened hinge pins
-Traxxas hardened shock shafts
-RPM rear carriers
-RPM front carriers (optional)
-RPM Arms (lighter than stock)
-Jato "mod 0.8" spur gears (56 & 58 tooth) & 32pitch or mod 0.8 pinions
-3mm hardware for converting the shock top screws to just studs
(3x30mm & 3x25mm & 3mm nuts)
-Traxxas aluminum shock caps
-Proline steering rack & aluminum servo arm
Other notes:
The stock Traxxas 2075 servo will not last forever.
With the Jato spur gears you can't run a gear cover, but you won't need it.
The gearing for the Jato spurs would be 56t spur & 13t pinion roughly for stock.
For hot modified motors the 58/10 will be the furthest down in gearing you can go.