I had the same type of thing happen but not where I had to slow to 25 mph. Anyhow, my issue ended up being a centerlink end. Replaced and realigned for $200 at a Ford dealer about 20k miles ago and all has been well.
BTW-My truck is stock except for 2.5" Front Levelers with Factory 20" Rims
Last edited by JohnF350Outlaw; 11-24-2010 at 12:48 PM.
Reason: Added BTW