Mystery vibration at 25 mph can't be diagnosed. It's not the front end!

slantsixdan don't give up on me now. It's all mine now. Yes you saved me 50% on 5-leaf conversion. Now, it's time to check the B&T. I do have the factory service manual you suggested. It tells me the exact torque on the front and back bolts of the driveshaft. Good info. I want to thank Pishta for the automatic trans converter bolts and flex plate information. I didn't know there was balance weights on the converter. That sounds right because it just starting doing this 3 or 4 months ago out of nowhere. It seems that something like balance weights were maybe flung off. Dart only shutters at 25 mph which is probably it's harmonic vibration that all cars go through when fired up cold. The shop was wrong. I ran it up in neutral and park and there was no vibration. When I picked it up, the owner conceded the fact that it is indeed a drive line problem. Good thing I stopped them from going any further. Yes, I will consider going to a 4X4 shop or drive line specialist to just dump the B&T if I feel that it is the problem after diagnostics.