Hi Colleen

The TR should not be a problem. Stefan Kiebel has written a paper describing corrections for slice timing within the DCM model. At the final stage of the DCM modelling you specify the timings of the slices where your data has come from. For example if you have an ascending sequence, 29 slices, and you have included a region from slice 15 then your timing would be approximately 1 second. You do this for each region of your model and DCM will take account of this in the estimation.
Note that if you have used an interleaved sequence then it is recommended that you carry out the slice timing as part of your pre-processing and enter the time for the slice you have interpolated to.

Hope this helps and good luck
Nia