Since it looks like you have taken it down to the bare metal in your pictures, you might as well go with the etching primer/filler primer route. DO NOT use an etching primer and then an epoxy primer as their chemical makeup are not compatible. As a general rule, use epoxy primer over old paint. Use etching primer when you go all the way down to the bare metal on the whole truck. Etching primer has a little bit of an edge over epoxy. Etching attaches itself chemically to the metal forming a very tight bond. Epoxy seals the existing surface and provides a uniform surface so that the boo-boos of the past don't have to be removed.
