There is known bug with the remaining work trends. Can you check if you don't have the same case?
Bug: Remaining work trend does not filter by iteration
- Create a project using the MS Agile template
- Add some iterations and ensure only one of them is "current".
- In each iteration, add some tasks and set the remaining work to some value.
- Open the dashboard and view the Remaining Work Trend graph
- Notice that the graph actually includes the remaining work from all tasks in the project instead of just the tasks in the current iteration.
- The timeframe of the graph in terms of what is shown on the X-axis is showing the correct dates, but the data points are wrong.
As for the Velocity report it is a feature request that I'll add but at the moment I can't give more concrete information as the Work Item Manager is not under active development anymore.
You can check out TeamPulse
if you haven't already. TeamPulse is a separate product that integrates with TFS. It also has its own set of reports, one of which is a burndown graph like the one in WIM, except that it calculates the burndown as you expect.