I have a 2008 silverado 2500HD 6.0 gas 6 speed auto with 6 speed
manual trans.
I have a cougar 326MKS at 9800lb I add another 1000lb with all
the storage this trailer has, get 9 MPG I do slow to 40mph going
over the grapevine,but that's a big hill most of the time have
no trouble doing the speed limit I drive in 5Th for most of the time
I leave it in manual so I can shift down for going down hills to save the brakes.