new 8.25 shudder in low speed turn

Per phone call to Dr. Diff I got the following tidbits, some of which he stated in a post above (thanks Doc!):
- cone-type sure-grip needs friction modifier just like clutch-type
- one bottle of friction modifier/additive is all you need
- Ford additive seems to stop chatter better than Mopar additive
- if it's chattering, the oil is contaminated; drain it and add new oil with the additive
- cheapo GL-5 oil is as good as the fancy stuff (80W90 is good for most US climates)
- after filling, "drive" the car on jackstands for a few minutes and then let it sit overnight to "set" the friction modifier before driving

I haven't driven the car yet, but the Ford stuff smells much worse than the Mopar stuff, so it must work better... I'll report back after I drive a little bit.