I towed a 12k 5er with my 6.4L Hemi, and, as most of you know, I was completely happy with the performance.
I was about 21,000# GCW and it did just fine. 5th gear at 2200 RPMs on the flats, and 2nd or 3rd at 5000 RPM plus on the steep grades, but able to hold 60 mph. On all but the steepest mountain grades, I could accelerate (albeit slowly) if I wanted to. I wouldn't judge the 6.4L Hemi based on the "Ike" video as that was completely the opposite of my experience.
If the TC you will be hauling will be ~6000# and you'll be adding another ~3500# behind the rig, you'll be at ~10K lbs.
I think you'll be fine.
This was my set up.
