89Vette,
My TNR was purchased from:
http://www.specmo.com
It is also available from:
http://modelelectronicsinc.com/home.htm
The TNR can be hard to get as most GM dealers will not sell them. My Hummer dealer said he could not even order them.
LasVegas,
Looking at your pics, my antenna is back away from the windshield a little more. It is mounted on that black screw in your picture that is about 1" toward the cabin. This puts mine back a little further. I dont think anything is loose, it does not act like that. Certain headings are solid, so I feel like it is blockage from the truck itself. I was concerned when I mounted it, that it was not as foward as I liked. It still works OK but I just think the GPS light is on more than it should be, hence, the reason I was asking others.
As far as the calibration, it is not off very far, but since the Radio does have a calibrate feature, I thought I could get it closer. But it does not seem to work, or I just don't know what I am doing, which is more likely. As I said previously, it does not seem to matter after I "calibrate" it, it goes back to where it was before I started.
Thanks,
Wendell