My 2016 Chevy 1500 5.3 pulls 12-14k worth of flatbed quite well actually on flat ground at sea level. Add in high profile of a TT and it will pull about the same as your 9000lb TT.
I wouldn't want to do it at altitude or steep grades, but the truck will handle it. You won't be the first one to the top of the hill.
The best for sure choice would be a HD pickup for better stability, especially given your lack of towing experience, but properly set up I personally wouldn't have an issue with that trailer in the flat lands.
You don't "need" a diesel but they're nice! You can tell the wife you need one....