I did extensive research on used diesel trucks and I would not touch a Ford diesel built before 2010. GM has had its problem years as well and other than the 2011 and later LML engines the safest one to get is the 2006-2007 (Classic version) GM/Chevy truck with the LBZ engine.
With an older Ford I would look for one with the v-10 gas engine and not the diesel. Very easy to find more posts about pre-2010 Ford engine problems, more than you could read in a lifetime.
With the earlier GM there were problems with the head gaskets and with fuel injection and both entail very expensive repairs in the thousands of dollars and are best avoided.