As I said quite some time ago, an ability to change resolution of TIMs stored in PSH files would really do here. However, I think the resolution should be set manually - AFAIR, Photoshop's TIM filter screws up resolutions that are not power of two by making them one or two pixels wider, though I never had an opportunity to find out if size is affected after saving TIM in such resolution... By the way, have you fixed the "skewed preview" bug?