No Overdrive

[Mitch R]

I made the mistake of buying a used transmission out of a friends car. Transmission works great except it won't shift into OD, no matter what. I can get TCC lockup in 3rd, but no overdrive. I have done some research and have found mention of a 4th gear shaft stripping out. Is there any tests I can do to verify that thats whats causing this, and how extensive of a project is replacing this shaft? Also does anyone have any other ideas as to what might cause this?

The car is a '95 Lumina and the donor transmission came from a '94 Cutlass Supreme, both with 3100s.

Thanks in Advance,
Mitch