I figured it out. When I got the directory tree to select the installation folder, I selected an existing folder - D:\TurboTax. The installation then made this into C:\Program Files\TurboTax\TurboTax. If I instead just click on the root D: drive, not a folder, it correctly interprets this as D:\TurboTax. The software does not allow you to directly key in the path. I guess selecting the root D: drive is what I have done previously, but didn't remember it this time.
