That electric fan looks like a cheap POS wal mart fan........no offense it really does look bad. You need about 4000 CFM of air flow to cool a high performance V8. BUT that still doesn't explain your highway over heating......unless it gets hot first and then never can cool off. I would start with the fan and add a shroud first. The mechanical fan might be a good idea. And if you do that, I would go with the Mopar Performance viscous fan package with a shroud. Lastly, all radiators AINT on the same level by a LONG SHOT. Did you get one of those Ebay chinkesium specials? Was it a chinkesium special from somewhere else? Those are hit and miss at best. Some cool great. Some won't cool from **** to shinola. One word on radiators. Griffin. If it runs hot with an appropriately sized Griffin in it, rest assured, you got another problem.
