Well, I think I narrowed down the stability issue with my F150. It seems my spring bars are inadequate now. Last year the trailers TW was 720# or so, and I have 800# bars. This was fine for the 2014 truck, but now my trailers TW has grown, I added a power jack to the front, along with more cargo in the passthrough which raised the TW up 100#, so I am exceeding the Spring bars.
I have to get a new hitch after all, so once that is done, I am hoping to have finally resolved this last issue.
Got to say though, the EB in this truck is a beast. 50MPH to 80MPH passing up a slight grade pulling a heavy trailer and it barely felt like it was working. It is one strong power plant, and the 6 speed trans is just so smooth. Heard the new 10 speed is even better, which if true helps both Ford and GM who share the design.