The following is based on content cut from Generals 2 and has not been confirmed by canon sources.
The Sandstorm is a light recon vehicle of the GLA.
It is a probable replacement of the Rocket Buggy, as both are rocket equipped vehicles, however due to the smaller rocket pod, it is most likely no longer expected to carry out a light-artillery/ hit-and-run role, rather it could be a cheap high speed anti-vehicle unit. Furthermore, its payload is less that what the rocket buggy had before.
The Sandstorm fires all of its rockets in a single salvo. It then needs to cool down, making the Sandstorm defenseless while reloading.
Allows the vehicle to repair outside of combat.
Once this upgrade is purchased, the Sandstorm can fire all of its rockets at once. However, this ability renders the Sandstorm unable to defend itself for a period of time.