2wd at 60mph.
The CV boot is actually shot on my front DS... The CV very well could be shot as well. I didn't even think about this being the culprit. I did find an NP231 at the local junk yard yesterday, but it's in a Saturday-only lot, so I'll have to wait until then to check it out.
I'm going to order a replacement CV head for the front DS and see if that makes it any better. Thanks for the tip!