Meghan, What procedure are you following to set up your panohead and how are you checking that the setup you end up with "works"? The whole process should not take hours: I set up my head in ten minutes or so. You want to locate the entrance pupil of the lens on the horizontal and verical axes of the head in order to avoid parallax effects. You can quickly establish the position of the entrance pupil in less than a minute just by looking into the lens with your two eyes, and with the back of the camera pointing at a bright window or light. Stop the lens down to f/16, say, using the depth of field button on the camera so that you see the aperture as a small disc illuminated by light transmitted through the viewfinder. Move a finger along the lens barrel until it appears to be at the same distance as the spot and that gives the approximate position of the entrance pupil. Use that position as the starting point for further tests to refine the position. See this tutorial.
Make sure you have the tripod sited on a solid floor and set the camera to a small aperture for your tests (e.g. f/11 - f/16). Since the lens has a longish focal length, I would use the method with a strip of sticky tape on a window described in the tutorial or two widely separated objects (poles etc).
I was following the method of finding the Nodal Point by using the gold ring. If I had read that tutorial earlier, I would have done the point the lens at light thing, and realized that the entrance pupil was much father back then the gold line on the 105mm lens.
That being said, I still don't think it would have only taken me 10 minutes...
I did figure it out though, later last night. If anyone else has rail settings to compare mine to, I wouldn't mind seeing if there is a big difference.
For the Bottom Rail, I'm using 63mm, and the Top Rail, 67.5mm.