Why does everything need to look different for something to be entirely new? They will all have four wheels after all. If something ain't broken don't change it radically. And yes, the interior is new with slightly more room and quite a few different amenities.
Seems like essentially every part of the drive train is changed except for the engine of the 4 cyl. The frame is entirely new as well. Materials changes on many parts of the body. Personally I think they kept what worked in the 2nd gen and made a lot of important changes under the skin. I'm really glad they didn't give it a wedgie with the ridiculously high bedsides most new models have been coming out with.
Anyway, was interesting to hear a few more details compared to the previous Q&A from months ago! Thanks OP for posting!
Though for me it is academic as I just bought a 2015 and don't plan on buying another truck until 2035 or later!