Graduate Assistantship is more or less similar to Research Assistantship. The work of a GA will typically include doing research and doing other departmental upkeep. There is no hard and fast rule about the work offered to a GA and depends on the department and the faculty. The work of a GA is important at the departmental level. In some universities, there is no difference between a GA and an RA.
The remuneration of a GA tends to be similar to an RA. You would get an in-state tuition fee, full or partial tuition fee waiver. Some well-funded departments do offer more stipends than RA.