The A310s were inherited from PanAm, for the most part, and were in pretty deplorable mechanical and cosmetic condition. Delta received a few A310s new from Airbus as well. The A310 proved to be costly and complicated to maintain, so Delta got rid of them. Where they went, I have no idea.
As far as the DC-10s, I don't think they were interrim aircraft as Iwantanl1011 stated - I've heard differently, but can't quite remember exactly what the situation was. I think these aircraft were also inherited; there were VERY few of them and they have also gone off to parts unknown. Probably for lack of fleet commonality, much like the A310s.
Anyone know anything more?