If you get the big bore shocks, they are essentially a aluminum version of the Ultra shocks that come from the factory on the slash.
Regardless of either one, you can lower the shocks with spacers that come with the slash shock accessory kit.
Just pull the shafts out of the shock bodies and add the spacers from the kit on the shock shaft inside the body. Re-assemble the shocks and they will be quite a bit lower and your truck will handle like its on rails.
You really only need the plastic Ultra shocks that come on the slash...but...
The essential upgrades are
Aluminum shock caps from Traxxas - prevents shock blow outs
Titanium Nitride coated shock shafts from Traxxas - smooths out shock travel
a multitude of different springs to swap out for different track conditions.
I gave you feedback when you purchased something
from me, so please return the favor.