I made pretty much the exact same move, older Kenwood to the 7300. The ATU thing you mentioned on 40m — are you running the end-fed with a matching unit at the feedpoint or just straight into the radio? I ask because mine was doing something similar and it turned out my 9:1 unun was the culprit not the radio ATU. swapped it out and 40 cleaned right up. might not be your issue but worth checking if you havent already.