Asking for a promotion or a demotion

Over the last year, I've had an increasing number of duties foisted on me that are not in my pay grade. Basically, I'm a level B worker, let's say, and I've been expected to take on tasks that level A workers handle-- mostly, lots of budget and contract-related troubleshooting and conflict resolution and decision making that I'd need to be promoted to in order to officially add these types of duties to my job description. From what I know, it takes staffers about 4-5 years to get promoted this way. I've been there less than 3 years. I'm getting sick and tired of being forced into these situations, which are often stressful and time consuming. At my level, I should be focused on producing certain products such as presentations and reports. Others at my level are never asked to take on the tasks that are often thrown in my lap, and they are much happier in their roles. I also know my section has budget and staffing issues. The person who used to handle a lot of these things is on indefinite leave and probably not coming back. I have a review in a few weeks and would like to present al of this. Is being asked to handle "A" level work enough to request a promotion? If I'm told no, I'd honestly like to be bumped down to the C level, even if it means a lower salary. The work is more pleasant and I may be able to move over to a different division that's less stressful. Thoughts? I could lose about $20-$30K by taking a demotion. The thing is, I just don't see getting off the crazy train, or being given an additional $30K to stay on the crazy train, anytime soon.